In this article, the effects of the “Void" of the contract as the origin of debt upon assignment contract have been analyzed in view of the Article 733 civil code.  Does the assignment contract become void when a contract related to the origin of the debt becomes void, or does it remain valid and the resulting obligations must be fulfilled? Additionally, with the annulment (becoming void) of the sale contract which is the origin of the debt, to whom should be returned the price obtained by the assignee (the assignor or the third-party assignee), and the third-party assignee may indicate to the assignor or assignee to return the price he paid; and also, to whom should the customer refer for the price (the seller or assignee). Using the descriptive-analytical research method and extensive study of Islamic jurisprudence and the analysis of Article 733 of the civil code, the study concluded that the void of the contract as the origin of debt causes the void of the assignment contract, and the assignee is obligated to return all things obtained illegitimately to the third-party assignee and the third-party assignee can choose whether to refer to the assignor or assignee in returning the price. This ruling applies to not only sales contracts, but any debt that is created through civil contracts or non-contractual events and an assignment is issued, and then it turns out that there was no debt; to begin with, the above rulings will apply.