Background & Objectives: Hospital wastes, when discharged into the wells and city sewerage system, leads to pollution of water resources due to their pathogen, drug, and toxic substances contents. So it has to be treated before discharge. The purpose of this study was determining the best coagulants before and after ozonation to pretreatment of the hospital wastewater. Methods: We used a laboratory system including ozone generator with the capacity of 15.5 go3/h, one liter reaction reactor and Jar-test system by using Alum, PAC, FeCl3 coagulants. Turbidity was tested based on standard methods. Results: PAC was determined as the best coagulant for before ozonation of hospital wastewater. Using 200 mg/Lit of PAC along with l mg/Lit of cationic poly electrolyte resulted in 99.2 percent of turbidity removal. Alum was the best coagulant for after ozonation with a dose of 200 mg/Lit along with 0.3 mg/Lit of cationic poly electrolyte that resulted in 97.98% removal of turbidity. Conclusion: PAC and Alum were determined as the best coagulants for before and after ozonation of the hospital wastewater, respectively. Ozonation reduced the dose of coagulants applied.