AIM: To observe the effect of ischemic preconditioning on cyclinD1 expression in rat liver cells during early ischemic reperfusion.METHODS: Fifty-four SD rats were randomly divided into ischemic preconditioning group (IP), ischemia/reperfusion group (IR) and sham operation group (SO). The IP and IR groups were further divided into four sub-groups (n = 6). Sham operation group (SO)served as the control group (n = 6). A model of partial liver ischemia/reperfusion was used, in which rats were subjected to liver ischemia for 60 min prior to reperfusion. The animals in the IP group underwent ischemic preconditioning twice for 5 min each time prior to the ischemia/reperfusion challenge. After 0, 1, 2, and 4 h of reperfusion, serum and liver tissue in each group were collected to detect the level of serum ALT, liver histopathology and expression of cyclinD1 mRNA and protein. Flow cytometry was used to detect cell cycle as the quantity indicator of cell regeneration.RESULTS: Compared with IR group, IP group showed asignificantly lower ALT level in 1 h to 4 h sub-groups (P＜ 0.05). Proliferation index(PI) indicated by the S-phase and G2/M-phase ratio [(S+G2/M)/(G0/G1+S+G2/M)] was significantly increased in IP group at 0 and 1 h (26.44± 7.60% vs 18.56 ± 6.40%,41.87 ± 7.27% vs 20.25 ±6.70%, P ＜ 0.05). Meanwhile, cyclinD1 protein expression could be detected in IP group. But in IR group, cyclinD1 protein expression occurred 2 h after reperfusion. The expression of cyclinD1 mRNA increased significantly in IP group at 0 and 1 h (0.568 ± 0.112 vs 0.274 ± 0.069, 0.762± 0.164 vs 0.348 ± 0.093, P ＜ 0.05).CONCLUSION: Ischemic preconditioning can protect liver cells against ischemia/reperfusion injury, which may be related to cell proliferation and expression of cyclinD1 during early ischemic reperfusion.