Research on hepatitis A vaccine produced from diploid cells cultured (MRC5) in Vietnam is necessary and is the current trend in the world. For vaccine development, adaptation strains HM175 in MRC5 cells is an important issue first, which determine the optimal temperature of strain HM175 on cell should be determined. Objective: Determine the optimal temperature of HAV HM175 strain on MRC5 cell culture. Method: cultured HAV HM175 strain on MRC5 cell at temperatures 32°C, 35°C and 37°C to select the appropriate temperature for virus multiply on MRC5. Using techniques titrated virus on cells to evaluate research results. Results: At a temperature of 35°C, strain HM175 replication on MRC5 cells with the highest. Conclusion: The optimal temperature of HAV HM175 strain on MRC5 cell culture is 35°C.