By the progress of the medical and surgical science, the possibility to change the people's sex from female to male and vice versa has been brought about and this change is made not only on the patients such as (bisexuals) but also on the healthy people. In this paper, the rules and consequences created by the sex-reassignment in the consanguineal and affinal relationships among the individuals have been discussed. The individual's sex is generally the criteria for the attachment of duties. In case the aforementioned has already been married, as soon as the sex-reassignment is occurred, the former contract of marriage will be invalidated or terminated according to certain conditions. The sex-reassignment of a man to a woman will cause the waiver of all periods on her and the husband will be obliged to pay her marriage portion completely.