One of the requisite of validity of a transaction is certainty and determination of transaction’s object. (accordance to part 3, article 190 civil law).We also see the same rule in Islamic law, that breach of these conditions, would cause risk and loss, and finally validity of contract.This discourse is putting in order in 3 sections as follows:In chapter 1, it will consider, the concept and effects of “determination of object”. we will see, doubt in offer stage, won’t be impediment to make a sale. In addition, it will consider, doubt in fungible and non-fungible thing, uncertain terms and sanction of uncetainty object.In chapter 2, that is entitled as “certainty of object” we will consider the concept, grounds, and domain of certainty.We will see there is difference, between the mistake in nature or quantity or qualification with uncertainty.In addition, it will consider the basis of neccessity of certainty object and public order and wise base will introduce as basis of necessity of certainty of object.At last, in this chapter, it will settle to distinction of those contracts, in which the general knowledge is necessary clause.