Background and Objectives: In 1997, a novel DNA virus, unrelated to the known hepatitis viruses, was isolated from the serum of a patient with post transfusion acute hepatitis with elevated alanine aminotransferase of unknown etiology, and it was named TT virus (TTV). In this study, the frequency of TTV and its role in induction of liver damages were evaluated in three groups of healthy, HBV and HCV-infected blood donors in Tabriz.Materials and Methods: In this descriptive study, sampling was done on 100 healthy donors, 40 HBsAg positive and 40 positive Anti-HCV in East Azarbayjan Blood Transfusion Center. The levels of ALT and AST in the sera were measured; DNA was then extracted and PCR was performed using T801 and T935 consensus primers. One-way ANOVA, Tukey-Kramer, Kruskal-Wallis, Dunn's and Fisher’s exact tests were finally used for statistical analyses.Results: TTV was detected in 65%, 70% and 67.5% of the healthy, HBV and HCV-infected blood donors, respectively. In each group of blood donors, the levels of ALT and AST were not significantly different in TTV infected versus non-infected individuals.Conclusions: Given the high frequency of infection in healthy individuals and considering the level of hepatic enzymes in TTV infected individuals, it seems that the virus or at least certain genotypes present have not been pathogenic for the infected individuals tested.