Abstract Background: Poor knowledge on the importance of hand washing and inaccessibility of hand washing facilities at institutional and individual level accompanied by different personal and environmental factors makes school children less likely to adopt hand washing practices which in turn have great impact on their health. There is limited information on knowledge on the importance and practice of hand washing among primary school children in Ethiopia, particularly in the study area. Objective: To assess knowledge on importance and practice of hand washing and its’ associated factors among primary school children the case of Debretabor town. Methods: Institutional based cross-sectional study was conducted from Oct. 29 to Nov.15/ 2018 in South Gondar Zone, Debretabor administrative town. Seven hundred ten study participants from 10 2nd cycle primary schools were selected by stratified random sampling techniques. Data was collected through face to face interview using pre-tested structured questionnaire by electronic data collection tools (smart phones) and observational check list. The collected data was analyzed using Generalized Estimating Equation by SPSS version 23.0 software. P-value less than 0.05 was considered to identify statistically significant variables. Adjusted Odds ratio (AOR) with 95% confidence interval was used to measure the strength of association between dependent variable and independent variables. Result: Two hundred fourteen (30.1%) of study participants in the 2nd cycle primary schools had proper hand washing practice. Three hundred seventy seven (53.1%) of 2nd cycle primary school children had good knowledge on importance of hand washing. Only four from 10 schools had adequate hand washing facilities and adequate water supply. From all predictors, adequacy of hand washing facilities, adequacy of water source at school and knowledge of study participants were strongly associated with hand washing practice as it was statistically evidenced by (AOR: 2.6, 95% CI: (1.7, 4)), (AOR: 5, 95% CI: (2.5, 9.4)) and (AOR: 1.6, 95% CI: (1, 2.8)), respectively. Adequacy of hand washing and availability of water source at school were predictors of knowledge on hand washing AOR: 2.3, 95% CI :( 1.2, 4.3) and AOR: 17.4 CI: 11.1, 27.2) respectively. Conclusion: This study revealed that only small proportion (30.1%) of study participant practiced proper hand washing. However more than half (53.1%) of the study participants had good knowledge on hand washing. Adequacy of school WASH facilities particularly hand washing station, water supply at school and Knowledge of study participants were significantly associated with hand washing practice. Adequacy of hand washing and water supply facilities at school were predictors of knowledge on hand washing.