2任分配实体法政策的研究。对于域外观点，我国可以借鉴的地方：一是要重视实体法政策对于无法律上原因举证责任分配的影响； 二是要设法减轻就无法律上原因负举证责任一方的举证负担。 第五章论述了各种类型不当得利无法律上原因的举证责任分配。 给付型不当得利可以分为狭义非债清偿和其他给付型不当得利。 对于狭义的非债清偿无法律上原因的举证责任分配，从维护民法安定性价值的实体法政策考虑，应该由原告就无法律上原因承担举证责任。对于其他给付型不当得利，无法律上原因或实质上为积极事实， 或可以通过对积极事实的证明达到目的， 因此由原告负举证责任，不存在证明的困难。对于非给付型不当得利，因为法律对财产发生转移的事由本身含有否定性评价，所以当原告证明了财产转移的事实后，推定被告取得利益没有法律上原因，被告否认的话，由被告就得利有法律上原因负举证责任。 关键词：关键词：不当得利 无法律上原因 举证责任分配 IAbstract The legal fact of unjust enrichment is constituted by four major elements, which are: the benefit, the damage, the causal relationship between benefit and damage, and lack of legal cause.For the allocation of the burden of proof of these four elements, the big controversy existing both in the theoretical research and in practice is which party should assume the burden of proof of “lack of legal cause“. This article includes five chapters to discuss the distribution of burden of proof of lack of legal cause. The first chapter mainly introduces the meaning of lack of legal cause. With regard to the meaning of lack of legal cause, there are two scholarly circles:unionism and non-unionsim.Unionsim includes fair, claims,legal relations and so on. But these theories are inadequate in the interpretation of the meaning of lack of legal cause. Non-unionism explore specific meaning of lack of legal cause of the specific types of unjust enrichment on the foundation of classification of unjust enrichment. It is easy to understand the meanding of lack of legal cause. In this chapter, specific meaning of lack of legal cause for various types of unjust enrichment is explained separately. Chapter II inspects the extraterritorial (including Germany, Japan and Chinese Taiwan region) views on the the allocation of the burden of proof of lack of legal cause of unjust enrichment. The allocation of the burden of proof of lack of legal cause vary in accordance with the type of the unjust enrichment.For the payment unjust enrichment, the plaintiff assume the burden of proof of lack of legal cause;for the non-payment unjust enrichment, the defendant assume it. If the plaintiff assume the burden of proof of lack of legal cause, it need to alleviate the burden of providing proof of plaintiff. Such as “indirect proof“ in Germany, “demand the defendant illustrate the specific causes“, “ the burden of proof by stage “, “the defendant would have obligation to state the reasons or even provide evidence“in Chinese Taiwan region. Chapter III describes the status about the allocation of the burden of proof of lack of lagal cause of unjust enrichment in our country. There are no legal and judicial interpretations explaining the allocation of the burden of proof of lack of legal cause. “Rules of Evidence“ tells the general rules of the allocation of the burden of proof, but whether the rules applying to the allocation of the burden of proof of the lack of legal cause is still in dispute. Scholars hold different views on the allocation of the burden of proof of lack of legal cause. For exmple, whether it need to classify the unjust IIenrichment,which party should assume the allocation of the burden of proof,what are the reasons for the allocation? In practice, there is also a dispute for the distribution of the burden of proof of lack of legal cause. For example,which party is easier to prove evidence, which party should be subject to a favorable presumption after the property transferring, whether the court could decide how to disribute the allocation of the burden of proof. Chapter IV compares the differences of allocation of the burden of proof of lack of legal cause between within and outside first. These differences are that, we don not study the allocation of the burden of proof of lack of legal cause of non-payment unjust enrichment ,and we don not give full consideration to the policy for lack of legal cause which affect the allocation of the burden of proof. The causes of these differences, include that, our theory as so as legislation of unjust enrichment are backwardness relatively, and we are lack of research on policy of substantive law which affect the allocation of burden of proof. From the extra-territorial views, we can learn that: first, we must attach importance to policy of substantive law of the allocation of the burden of proof of lack of legal cause; second, we should try to alleviate burden of providing proof of who assume burden of proof. Chapter V discusses the the allocation of the burden of proof of lack of legal cause of various types of unjust enrichment. Payment of unjust enrichment can be divided into narrow condictio indebiti, and other types of unjust enrichment. For the narrow condictio indebiti, the burden of proof of it should be assmued by the plaintiff because of maintainning the stability which is an important value of substantive law. For other payment type of unjust enrichment, lack of legal cause substantially are positive facts, or can be proved by proving positive fact. So there is no difficulty for p