To observe the effects of LDR on the p38 MAPK expression and the secretion of IL-12 in J774A.1 cell line, we used ELISA and flow cytometry to examine the changes in these two specialities. Results showed that IL-12p70 in J774A. 1increased 2-8h after 75mGy X irradiation, and consistently, p38 MAPK expression increased at the 2nd h after exposure. Both of these increases showed statistic significance. Conclusions were drawn that LDR might stimulate IL-12 expression , and p38 MAPKmight play some role in the activation of IL-12, which would provide theoretic basis for the hormesis effect of LDR.