Background: Prolonged length of hospital stay is the most common indicator of poor quality of health care and inefficient utilization of hospital resources. Prolonged hospital stay associated with increased mortality, hospital-acquired infection, and unnecessary utilization of hospital bed and other resources. Predicting length of hospital stay facilitates resource designing and initiates quality improvement activities. However, data regarding the prolonged length of hospital stays, and associated factors were a scarce in Ethiopia. Objective: To assess prolonged length of hospital stay and associated factors among adult patient admitted at surgical ward of selected public hospitals in Arsi Zone, Oromia, Ethiopia, 2022. Methods: A hospital-based cross-sectional study was conducted on a sample of 316 adult patients from December 1 to January 10, 2022. A consecutive sampling technique was used during sampling procedure. A structured questionnaire was used to collect data regarding sociodemographic factors, clinical factors, medication factors, and behavioral factors through interview, medical record review and by using check list. The data was entered into the epidata4.6 version and exported to SPSS Version25 for binary logistic regression analysis. To identify factors associated with outcome variable, candidate variables (p<0.25) were fitted to multivariable analysis, and those with P-values<0.05 were considered as factors associated with prolonged length of hospital stay. An odds ratio with corresponding 95% CI was used to indicate the strength of association of variables with prolonged length of hospital stay. Result: Seventy eight (24.7%) of the patients experienced a prolonged length of stay at surgical ward. The odd of a prolonged length of hospital stay was high among patients who had comorbid condition [AOR=4.59, at 95% CI= (2.46-8.56)], who undergo elective surgery [AOR=3.98, at 95% CI= (1.11-14.33)], who developed surgical site infection [AOR=5.02 at 95% CI= 1.97-12.80)], and who developed hospital acquired pneumonia during hospital stay[AOR= 3.43 at 95% CI= (1.36-8.64)]. Conclusion: About 1/4th of the study participants have prolonged length of stay at the surgical ward. Comorbid condition, elective surgery, surgical site infection, and hospital acquired pneumonia are factors associated with prolonged length of hospital stay at the surgical ward.