Objective:To investigate the potential influence of IL-29 on the expressions of protease activated receptor(PAR)-1,2,3,and 4 on the membrane and in the cytoplasm of P815 mast cells. Methods:After being challenged with various concentrations of IL-29 for 2 h,6 h and 16 h, the P815 mast cells were collected and treated for flow cytometry to detect the membranous and cytoplasmic PARs expression. Results:Compared with the corresponding control,expression of PAR-1 induced by IL-29 was significantly decreased either on membrane or in cytoplasm of P815 cells, and the difference between membranous and cytoplasmic PAR-1 expression induced by IL-29 was not significant. IL-29 did little effect on the expressions of PAR-2,3,4 either on the membrane or in the cytoplasm of P815 cells as well as the corresponding control,though the differences between membranous and cytoplasmic PAR-2,3 and 4 were significantly detected. Conclusion:IL-29 can down-regulate the membranous and cytoplasmic PAR-1 expressed by P815 mast cells but has little effect on the expression of PAR-2,3 and 4 either on membrane or in cytoplasm of P815 cells. Though significant differences between membranous and cytoplasmic PAR-2,3 and 4 are present, either membranous or cytoplasmic PARs expression is representative while flow cytometry can be used to detect IL-29 modulating PARs expressed in P815 mast cells.