Abstract: In this study we explored the expression of Hyriopsis schlegelii Cyclophilin A in response to infection and the effect of this protein on the growth of Hela cells. The mRNA level of this gene in the haemocytes, liver and gonad was measured with Real-time PCR after the Aeromonas hydrophila challenge. It was observed that the transcription of HsCyPA in haemocytes, gonad and liver was significantly up-regulated at 4h after the challenge and then decreased at 8h. These results suggested that HsCyPA might be involved in the immune response. The complete ORF of HsCyPA gene was subcloned into pET-32a (+) prokaryotic expression vector, and then expressed in E. coli BL21 (DE3). After the optimization of induction conditions, the soluble fusion protein was purified with Ni-NTA affinity chromatography. To test the effect of this recombinant protein on Hela cells, we diluted it into certain concentrations (50, 100, 200, 400, 800 ng/mL) and applied them into Hela cell strains through MTT assay. It was revealed that the recombinant HsCyPA could promote the proliferation of Hela cells, and the proliferation rate reached the maximum (18.5%) when the HsCyPA concentration was 100 ng/mL. These preliminary results indicated that Cyclophilin A could be a multi-functional protein which might participate in immune responses and cell growth regulation.