Background: Each year 4.2 million people around the world die within 30 days of surgery and postoperative deaths account for 7.7 % of all deaths. So this study aimed to asses’ magnitude of postoperative mortality and associated factors among patients who underwent surgery in Wolaita Sodo University Teaching referral Hospital.Method: Retrospective cross sectional design was carried out from April 15-30 2019. Card review was done on 384 participants by using Systematic sampling technique. Entered to Epi Data; exported to SPSS for analysis. Variables with p-value < 0.25 in bivariate analysis were entered to multivariate logistic regression. Statistical significance is determined at p-value < 0.05.Results: The magnitude of postoperative mortality was 5.7%. Using surgical check list (AOR= 0.18; 95% CI 0.05 to 0.61), having comorbid condition (AOR= 4.45; 95% CI 1.39 to 14.19), and don’t having blood transfusion (AOR= 0.07; 95% CI 0.02 to 0.22) and general anesthesia (AOR= 4.37; 95% CI 1.17 to 16.30) are factors of post-operative mortality.Conclusion: The magnitude of postoperative mortality was high. Surgical check list, comorbidity, blood transfusion and general anesthesia are factors. The hospital should encourage using of surgical check list and work on comorbid patients to decrease the mortality. Keywords: Magnitude; mortality; surgery; post-operative; Wolaita.