Background: The first two years of life are a critical window for ensuring optimal child growth and development. Delayed complementary feeding practice severely affects the physical, cognitive, and economic development of the child and the nation. So, this study was aimed to identify late practices of appropriate complementary feeding and associated factors among mothers of children aged 6 - 23 months. Objective: To assess prevalence of late initiation complementary feeding practice and associated factors among children aged 6-23 months in Ayehu Guagusa district, Amhara region, Ethiopia. Method: A community based cross sectional study was conducted among 451 mothers with children aged 6-23 months in Ayehu using systematic random sampling technique. Data was collected through face-to-face interview using structured questioners. Data entry and analysis was conducted using Epi Data version 3.1 and SPSS version 23 software respectively. Frequency and cross tabulation were conducted to describe relevant variables in relation to the outcome variables. P-value less than 0.05 with 95% confidence level was used during multivariable logistic regression analysis to identify significant determinants of late complementary feeding practice. Results: The response rate was 100%. The prevalence of late complementary feeding practice was 54.1% (95%CI:50.1, 59.2). Increasing maternal educational status (AOR:0.193,95% CI: 0.071-0.525), home delivery(AOR: 7.113, 95% CI: 2.766-18.293), decreasing birth order(AOR:0.038,95% CI :0.005-0.303), knowledge know to start complementary feeding(AOR: 0.80, 95% CI: 0.041-0.157), decreasing number of children(AOR=22.574, 95% CI: 2.74-185.98) and presence of husband support( AOR: 0.206, 95% CI 0.112-0.380) were found to be independent predictor of late initiation of complementary feeding practices. Conclusion: The prevalence of late complementary feeding practice is high as compared study conducted different parts of country. The predictors of late initiation of complementary feeding practice were number of children, birth order, knowledge about time to start complementary feeding, husband support, place of delivery and maternal educational status. Key words: Late complementary feeding practice, Initiation of complementary feeding, Complementary feeding practice