Objective: The purpose of this study was to evaluate the family function perception and socialsupport levels of mothers of the children with Down syndrome.Methods: This descriptive study was conducted in seven private education and rehabilitationcenters affiliated to three District National Education Directorates in city centers between 15March 2012 and 28 February 2013. The study was conducted with mothers of 63 children withDown syndrome, who accepted to participate in the study, without using the method of samplegroup selection. The data were collected using the Questionnaire, Family Evaluation Scale, andMultidimentional scale of the perceived social scale. Percentiles, means, Kruskal-Wallis test,Mann-Whitney U test and correlation analysis were used to assess the data. Results: Evaluating the relation between the perception of the family functions and the percei-ved social support; it was determined that regarding family function perception of mothers,there was a significant inverse relation between their scores of subscales Problem Solving , Communication , Roles , General Functions and their total score. There was similar rela-tion between their scores of social support dimensions of Perceived from Family, Friend and aSignificant Other and their total social support score.Besides, there were significant inversecorrelations between scores of the Affective Involvement and Behavioral Control subscalesof the perception of family functions and scores of the social support dimension of perceivedfrom the family, a significant other and total score. Conclusion: The results revealed that mothers of the children with Down syndrome fulfill theirfamily functions, while the mothers having higher levels of social support carry out the familyfunctions more effectively.