This research wants to find out the character and function of mamak (the maternal uncle) and ninik mamak (the adat chiefs) and also the background their depiction in Sitti Nurbaya and Anak dan Kemenakan by Marah Rusli. The theoretical framework which is applied in the research is sociology literature approach. The application of this theory in this research based on the point of view that literature is a social and cultural product that could be able to analysis with the social and cultural approach. Literary work, then, cannot be fully understood apart from the milieu or culture in which it was produced. It must be studied in the widest possible context. Every literary work is the result of a complex interaction of social an cultural factors.The conclusion of this research states that the depiction of mamak and ninik mamak of Sitti Nurbaya and Anak dan Kemenakan are different from the concept of them according to Minangkabau's custom. Mamak and Ninik mamak are two important elements in whole Minangkabau social structure. They have responsibility in daily life of their own matrilineal kinship group. They also have to respected to the adat regulation. In Sitti Nurbaya and Anak dan Kemenakan, mamak dan ninik mamak are depicted in the atmosphere conflict between those who wishes and disires to keep the tradition and those who wishes an improvement in apply of adat.The depiction of the character and the function of them is influenced by several factors. Firstly, the background of the writer. Marah Rusli came from the coastal lowland of Minangkabau (Rantau) which it has differentiation in social culture from the interior highland (Darat). Secondly, Sitti Nurbaya and Anak dan Kemanakan are published by Balai Pustaka which it had several clafication and wisdom in publishing literary work. Thirdly, the social history influences. The education aspect has a stimulating effect on awakening Indonesia young generation's consciousness in their life. Marah Rusli, one of the Indonesia young writer, was influenced by the time and his education and wishes an improvement in application of adat system in society.