Fate of tricyclazole in rice paddy system was studied. The effect on soil microorganism as well as the mutagenicity of the compound was also examined. The residues of tricyclazole in crops and soil with two times application before harvest were 0.37 in unpolished rice, 0.29 in polished rice, 0.14 in rice straw, and 0.15 ppm in paddy soil. With three times of application the residues were increased to 0.46, 0.39, and 0.19 ppm, respectively. Until $2{sim}3$ weeks after treatment of pesticide the degradation of tricyclazole was progressed comparatively but very slowly afterward and the half life of that was about $140{sim}180$ days. There was no effect for viable count of soil microorganisms and for mutagenic test by Salmonella and Saccharomyces systems.