Abstract: Effects of five herbicides on the microbial activity, nitrification and animo-nification in two soils were studied.The results showed that the herbicides had little effects on soil microbial activity when normal amounts were applied in the soils, if there was any effect, it was temporal and would recover very soon. The results also showed that when the concentration of herbicides in soils was 1000 ppm, soil nitrification rate was inhibited but soil ammonification rate was stimulated in certain levels.The results will be valuable for selecting suitable herbicides as soil nitrificatron inhibitors, producing new fertilizer and herbicide mixture, increasing the efficiencies of fertilizers, decreasing the loss of nitrogen fertilizer and controlling the pollution.