This article discusses, through the study of the case of the Chilean Socialist Party (PS), the topic of party factionalism in the Chilean political system. First, we argue that the main internal groups of the PS might be considered as factions according to the most used definitions in the literature. Second, we discuss the relationship between the binominal electoral system and the factionalism in the PS. Third, we analyze the role of the factions in decision making processes of the PS, and maintain that there is a high degree of correlation between the internal electoral power of factions, and the number of parliamentary candidates each faction is able to present. This correlation is also high when we talk about the presence of the different factions in presidential cabinets.