Objective To investigate the immunoregulatory effect of sirolimus on the xenotransplantation with arterial patch. Methods The xenotransplantation of arterial grafts was taken from the wild-type Bama pigs to cynomolgus monkeys. The peripheral blood mononuclear cells of recipient monkeys at 14 days after xenotransplantation (POD14) were selected as subjects. Dimethyl sulphoxide (DMSO) was used in the control group (volume ratio of 1:1 000) and sirolimus was administered in the sirolimus experimental group (final concentration of 0.1 μmol/L and 0.5 μmol/L). The cells were cultured for 1.0 and 5.5 d, respectively. The activity of POD14 cells was evaluated. The DMSO control and sirolimus experimental groups (final concentration of 0.1 μmol/L) were established and cultured for 5.5 d. The quantity of T and B cells in POD14 cells was counted and the expression levels of cytokines and messenger RNA (mRNA) were quantitatively measured. Results Compared with the DMSO control group, the activity of POD14 cells was significantly decreased after sirolimus treatment at a final concentration of 0.1 and 0.5 μmol/L for 1.0 d (P<0.01-0.001). After sirolimus treatment at a final concentration of 0.1 and 0.5 μmol/L for 5.5 d, the activity of POD14 cells was significantly decreased (both P<0.001). Compared with the DMSO control group, the quantity of CD3+CD4+T cells and CD3+CD8+T cells in POD14 cells was significantly reduced after sirolimus treatment at a final concentration 0.1 μmol/L (P<0.05-0.01), whereas the quantity of CD3-CD20+B cells was considerably elevated (P<0.01). Compared with DMSO control group, the levels of interferon(IFN)-γ, interleukin(IL)-2, IL-4, IL-5 and IL-6 in the sirolimus experimental group were significantly down-regulated (P<0.05-0.001). The expression levels of IFN-γ, tumor necrosis factor(TNF)-α, IL-2, IL-4, IL-5 and IL-6 mRNA were significantly down-regulated (P<0.05-0.001). Conclusions Sirolimus inhibits the proliferation of POD14 cells in the recipient monkeys after xenotransplantation with arterial patch. The underlying mechanism is that the sirolimus can reduce the quantity of T cells and suppress the expression and secretion of immune rejection-related cytokines.