The study investigated family support and self-mastery as predictors of assertiveness among undergraduate. One hundred and thirteen (113) participants which comprised 70 females and 43 males between the ages of 24-50 years with a mean of 13.43 and standard deviation of 2.54, were selected from Enugu State University of Science and Technology (E.S.U.T), with the aid of purposive sampling techniques from the following faculties; Social Sciences and Humanities (45), Management Sciences (37), Law (31). The study was a cross-sectional survey in which Spencer (1973) Rathus Assertiveness Scale (RAS), Uddin and Bhuiyan (2019). Family Support Scale and, Pearlin and Schooler (1978) Pearlin Self-Mastery Scale, were used for data collection, while linear regression was used for analysis. Three hypotheses were tested and the results revealed that; family support Stβ= .434*** and t= 3.932*** positively predicted assertiveness among undergraduates at p< .001. Self-mastery Stβ= .249* and t= 2.256* positively predicted assertiveness among young adults at p< .05. Family support and self-mastery jointly predicted assertiveness at at p< .01. In view of the findings of the study the researcher discussed the result and recommendations were made.