Family is a social-biological institution and it is one of the most fundamental institutions of society. This article explores the structure of the family institution in Iran at the historical period from the Taherid dynasty to Mongols, to analyze the impact of the bondswomen on twofold function of the family. The family is taken into consideration as the institution which has been provided the individual’s emotional- sexual needs and the social- cultural security for reproduction and training children. In this regard, the paper seeks the functional roles of the bondswomen and the free women and it also goes through the other tasks of the bondswomen in the family institution to examine if there are any relations between the superabundance of the bondswomen and changes in family system