Family, as a social institution or group, has been evolving throughout history. Evolution of Family needs to be studied in order to understand its functions and Structure. Unfortunately, the evolution of Family during the long Iranian history has not been studied seriously. This paper is an effort to shed some light on the Structure and functions of the Iranian Family under Sassanids using documentary method. The findings reveal that the dominant form the Family in this period was “ extended Family” which along with the religious and political institutions constructed the Sassanid society. The Family Structure in this era was patriarchal, polygamy was prevalent, and ingroup marriages were preferred. The official religion of the empire, Zoroastrianism, viewed Family as a sacred institution with its main function as reproduction. Other functions of the Family were production and provision of economic support, socialization and education of offsprings, who had to inherit their father and mother’ s jobs. Relatives of father, in this period, had superiority to the relatives of mother’ s side, and the oldest son and his Family lived with his parents.