Background:This study intended to clarify the determining factors of complementary feeding practices among Tehran 6–24 months failure to thrive children in order to use the results for planning the interventions to reduce the possible adverse effects.Materials and Methods:In this study, 132 mothers of three medical and health centers were chosen by random sampling among those centers operating under the supervision of south of Tehran District Health Center and study data were collected from them. A valid and reliable questionnaire as a data collection instrument developed based on behavioral analysis phase of PRECEDE model. Spearman and Pearson's correlation coefficient test were used to determine the statistical relationship between factors associated with complementary feeding practices among mothers.Results:The mothers’ knowledge was as follows: 0.8%, 20.4%, and 78.8% of them were good, medium, and poor, respectively. Mean scores for the mothers’ performance in terms of supplementary feeding was 66.8. Pearson correlation indicated a positive and significant correlation between the mothers’ performance with enabling and reinforcing factors, but there wasn’t any significant relationship between the mothers’ performance and knowledge about complementary feeding.Conclusions:According to the obtained results, reinforcing factors, and enabling factors are associated with the mothers’ performance in terms of complementary feeding. Hence, attention to these issues is essential for better health interventions planning.