Introduction: Complementary feeding plays a vital role in growth and development of children and prevention of malnutrition. Objective:To determine the predictors of complementary feeding in 6 to 18-month-old infants and young children based on the Health Belief Model (HBM). Method:This cross-sectional study was performed on 270 mothers of children aged 6 to 18 months who were randomly selected from those referred to six health centres in Andimeshk city, Iran. Data were gathered using a 53-item questionnaire based on the HBM and were analysed by SPSS statistical software, descriptive statistics, Pearson correlation and multiple regression tests.Results: Mean age of the mothers was 29.8 ± 5.08 years and most of them were homemakers (88.5%) and had an under-diploma education (62.2%). The HBM constructs predicted a total of 28.9% of the variance of mothers' behaviour in relation to complementary feeding in children. Perceived selfefficacy (p = 0.001) and perceived barriers (p = 0.011) significantly predicted the behaviour. Conclusions:Perceived barriers and perceived self-efficacy are the most important determinants of mothers' behaviour in relation to complementary feeding in children.