Background –complementary feeding is the process of starting feeding the child other foods and liquids when breast milk alone is no longer sufficient to meet the nutritional requirements of infants, along with breast milk. Objectives -To assess knowledge, attitude and practice of mothers with children 6-23 months old on complementary feeding and associated factors, in B/Dar Zuria Woreda, Northwest Ethiopia. Methods- A community-based cross sectional study design wasused. A total of 631mothers’ with 6 to 23 months children- aged were included in the study. Data were collected by structured, pre tested questionnaire and multistage sampling method was used to select the participants. The degree of association between independent and dependent variables was assessed using odds ratio with 95% confidence interval and significance was declared at p-value <0.05. Result: About 585 mothers were interviewed making a response rateof 92.7%. The magnitude of good knowledge, attitude and practice of mothers on complementary feeding were 51.3%, 43.6.1% and 53% respectively. Marital status [AOR=2.299; 95% CI: 1.27, 4.163)], educational status [AOR =1.664; 95% CI: 1.047, 2.646)] and ANC follow up[AOR = 2.091; 95% CI: 1.19, 3.674)] had significantly associated with knowledge of mothers on complementary feeding.Age of mothers [AOR = 2.139;95% CI: 1.235, 3.705)], Educational status [AOR =2.414; 95% CI: 1.498, 3.889)], and number of under-five children [AOR =0.565; 95% CI: 0.361, 0.885)],had significantly associated with good Attitude of mothers on complementary feeding. On the other hand and child age [AOR = 1.742; 95% CI: (1.0, 2.809)],child age difference with [AOR = 1.634; 95% CI: (1.007, 2.652)] and household income [AOR = 0.428; 95% CI: 0.28, 0.654)] had significantly associated with good practice of mothers on complementary feeding. Conclusion: This study showed that the knowledge and the practices of the mothers towards complementary feeding were good. Even though mothers had good knowledge, their attitude had not been good due to different factors. Recommendation: Complementary feeding education targeting behavioral change especially among unmarried and uneducated mothers is important to reduce malnutrition.