Background: - Harmful traditional practice is a major contributing factor for Obstetric complication and it is highly practiced in Ethiopia. It has significant drawbacks leading women and children to different forms of morbidity and mortality during pregnancy and delivery. Therefore, the aim of this study was to assess the magnitude of harmful traditional practice and associated factor during pregnancy and delivery in Basketo special woreda, SNNPR Ethiopia. Method: - Community based cross-sectional study design was used to conduct this study. The study period was from March 1- June 30, 2013. The total sample size was 569 women of reproductive age group. Multistage sampling technique was used and the data was collected through face-to-face interview. Data was entered and analyzed using SPSS version 21. Multivariable logistic regression analysis was done to identify independent predictors of harmful traditional practice at 95% confidence level and P < 0.05 was used to determine statistically significant predictors. The result was expressed by using table, pie chart and bar graphs. Result: - Among the total participants, 29.5% and 33.4% mothers practiced harmful traditional practice during pregnancy and delivery respectively. This study identified food prohibition (9.8%), drinking of kosso (2.4%), home delivery (34.6%), and application of substance on the cord stump (26.9%) as the major harmful traditional practice. Age (AOR: 6.1, 95% CI: [2.117.99]), being rural dweller (AOR: 11.16, 95% CI: [3.95-31.56]), being illiterate (AOR: 24.84, 95% CI: [3.24-190.3]), duration of stay in that kebele (AOR= 1.97, 95% CI: [1.1-3.61]) and being grand multigravida mothers (AOR: 0.44, 95% CI: [0.20-0.97]) were significantly associated factor for harmful traditional practice during pregnancy. Being aged (AOR: 3.45, 95% CI: [1.34-8.87]), rural resident (AOR: 26.28, 95% CI: [8.83-78.19]), being Merchants (AOR=14.3, 95% CI= [1.71-119.24]), duration of stay in kebele (AOR: 2.24, 95% CI: [1.014.95]), time to reach health facility (AOR= 0.49, 95% CI= [0.30-0.82]) and maternal knowledge (AOR:0.31, 95% CI: [0.18-0.55]) were significantly associated factor for harmful traditional practice during delivery. Conclusion and Recommendation: - harmful traditional practice during pregnancy and delivery are highly prevalent and our study highlights that age, residence, family size, duration of stay in the kebele, time to reach health facility, number of pregnancies, maternal educational status and maternal knowledge were predictive of harmful traditional practices. Therefore, an appropriate xiii implementation strategy that targeting at community health education and behavior change messages are recommended by considering those determinants needed to improve maternal health.