Confirmation of economic relations and providing the trust of contract parties in financial relations is vital for today’s complicated society, because economic opportunities are restricted and costs of investments are very high.

Deposit in commercial contracts is paid on the one hand to prove the good faith of customer in his / her intention to make the contract and on the other hand cash guarantee for fulfilling his / her obligation to make a contract and paying the rest of price. In these terms the seller is sure that he /she can compensate for damage suffered.

Although the goal of paying deposit in encouraging the  other party to do the pre arrangements or stages of contract in many legal systems has known nature and rules , this legal establishment has not clear nature both in common and legal system of our society .

In this thesis I tried to make a known the nature of deposit in Iranian Law concerning the nature of it in the Iranian common Law and fiqh and English and Egyptian Law and finally I suggested a section to make clear its position.

We can say about the nature of deposit in Iranian Law that payment of deposit doesn’t mean that the contract is voidable and parties of contract are bound to do obligations under paying the deposit unless the parties declared against it or they implied against it. When each party of contract avoids doing his / her obligations and binding him / her to do them is impossible  , if he / she is customer , he / she will lose the deposit and if he / she is seller he / she has to pay the deposit and the same amount of money to customer .