Abstract: Objective To investigate the subcellular localization of ATP synthase b subunit from Clonorchis sinensis under different conditions of Hela cell cycling, and the effect of this protein on the expression of its encoding-gene and homologous host genes. Methods pEGFP-N1-CsATP-synt_B and the vector pEGFP-N1 were transfected into Hela cells, respectively. Transfected cells were synchronized in G₀/G₁ by serum starvation, G₁/S, S cells by double thymidine block, and G₂/M cells by thymidine-Nocodozale block. After synchronization, the subcellular localization of the expressed fusion protein was observed with a laser confocal microscope. The expression level of this fusion protein in cells was detected by flow cytometry (FCM). The expression of CsATP-synt_B and HomoATP-synt_B in different cell cycle phases accessed by RT-PCR. Results FCM results indicated that in the G₀/G₁ phase the expression of pEGFP-N1 vector was decreased significantly, while pEGFP-N1-CsATP-synt_B expression showed an upward trend. In the other phases of cell cycle, the protein expression was similar in the above two kinds of plasmids. The intact CsATP-synt_B was expressed in mitochondria in the G₀/G₁， S， and G₂/M phases and nucleus during G₁/S phase. After the fusion proteins entered the nucleus, the mRNA expression of CsATP-synt_B and HomoATP-synt_B increased significantly. Conclusion CsATP-synt_B can be expressed in the nucleus during G₁/S phase, and regulated by the cell cycle and energy requirements.