Objective:To study the significance of human herpesvirus type 6B (HHV-6B) infection on human T-lymphoblastoid cell line Molt3 and its effects on cell cycle and proliferation. Methods:HHV-6B-infected Molt3 cell morphology was assessed by a inverted microscope. The fragment of HHV-6 U22 gene in Molt3 cells was amplified by PCR. Expression of HHV-6B late protein was examined by the immunofluorescence assay and Western Blot. Cell proliferation was measured by MTT assay after HHV-6B infected Molt3. Cell cycle analysis was evaluated by flow cytometry. The mRNA levels of cell cycle related protein were examined by Real-time PCR. Results:Molt3 cells infected by HHV-6B showed typical cytopathic effect at 48 h post-infection. HHV-6 U22 gene was detected by PCR. HHV-6 late protein was positive in infected cells by indirect immunofluorescence and Western Blot assay. MTT assay detected that HHV-6B infection inhibited the proliferation of Molt3 cells significantly. Compared with the uninfected cells,percentages of Molt3 cells infected by HHV-6B were increased in phase G1 but decreased in phase S and G2. The mRNA levels of cyclinE1 were decreased after 48 h post-infection,however,the mRNA levels of p53 were significantly increased after infection. Conclusion:HHV-6B can infect the Molt3 cells,lead to typical cytopathic effect,and inhibit cell proliferation and make the cell cycle stay in phase G1.