BACKGROUND: Prevalence of optimal complementary feeding practices are lower than expected. Undernutrition contributes 35% of children mortality. Our study was aimed to assess magnitude and factors associated with optimal complementary feeding practices among children 6-23 months in Bensa Dstrict, Sidama Zone, South Ethiopia, 2016.METHOD: A community based cross sectional study was conducted from January to February 2016 in (8) randomly selected kebles found in Bensa District. Respondents were selected by using simple random sampling technique after sampling frame was prepared from rapid survey. Pre-tested questionnaire was used to collect information. Then, data were entered into SPSS version 20, Then, crude odds ratio (COR) and adjusted odds ratio (AOR) with 95% confidence interval were computed to examine statistical significance. RESULT: This study revealed that only 8.6% (95%CI: 6.4, 10.7%) of 6-23 months children had optimal complementary feeding practices. Mother’s knowledge on optimal complementary feeding (AOR=5.4, 95%CI: 2.7, 11), postnatal care service utilization (AOR=3.4, 95%CI: 1.7, 7), and household food security (AOR=5, 95%CI: 2.5, 10.5) were positively associated with optimal complementary feeding practices.CONCLUSION: Mother’s knowledge, postnatal care utilization and household food security positively affected optimal complementary feeding practices.Thus, Bensa District Health Office, Sidama Zone Health Departiment and other respective stakeholders should cooperatively work to enhance knowledge of mothers/care takers on optimal complementary feeding practices, household food security  and on advantages of postnatal care service utilization.KEYWORDS: Complementary, feeding, optimal