Background: Waiting time remains a vital indicator among several tools for patient’s satisfaction in the health services organization. This is the case in most of the hospitals in Ethiopia, hence there was no study conducted in Tibebe Ghion Specialized Hospital and limited study in Ethiopia to assess factors affecting waiting time there need to conduct study on patients waiting time and identifying factors which affect waiting time at outpatient departments in Tibebe Ghion Specialized Hospital. Objective: To determine the length of patients waiting time and associated factors at out-patient department of Tibebe Gion Specialized Hospital (TGSH), Bahir Dar, Northwest Ethiopia, 2021. Methods: Institution based cross-sectional study was used from March - April, 2021. Proportional allocation to each OPD were done and A total of 417 patients were selected using systematic sampling technique were done. Data were collected using a time observation checklist together with interviewer administered structured questionnaire. Data were entered in to Epi data version 3.02 and exported to SPSS version25 for analysis. Waiting time was measured in each sections. Linear regression analysis was done to identify factors associated with overall patients waiting time. In multivariable regression analysis all variables with p-value of < 0.05 taken as significant association with overall waiting time. Results: A total of 395 patients were participated in this study with a response rate of 94.72% from planed 417 patients. The measured mean waiting time in this study was 219.98(95%CI: 210.02, 229.95) minutes (3.6 hours) with (SD +100.75 minutes (1.6 hours). Being a governmental employ reduced waiting time by 28 (B=-28: 95%CI: -52.9, -4.7) minutes as compared to farmers. Waiting time was reduced by 27.6(B=-27.6: 95%CI: -46.2,-9.1) minutes among patients who have previously visited the facility compared to new patients. Patients who were arrived afternoon increased the waiting time by 22.30(B=22.30: 95%CI:-41.93,-2.67) minutes compared to patients who were arrived in the morning. Also, Patients who arrived on Friday reduced the mean waiting time by 50.48(B=-50.40: 95%CI-78.1,-22.8) compared to who were arrived Monday. Patients who were satisfied reduced waiting time by 43.1(B=-43.1: CI-61.95,-24.2) as compared to patients who were dissatisfied. Conclusion: The waiting time among patients attending in TGSH was very far apart from WHO threshold. There for policy makers and interested parties might draft strategies targeting on patients who are illiterate, government employ, new, patients who come on afternoon, Friday, and those who are satisfied. Key words: waiting time, outpatient department, TGSH, factors, Northwest Ethiopia.