The effect of repeated chlorothalonil applications on its persistence and soil microbial activities were investigated in planted soil under greenhouse conditions. The results revealed that suppressed dissipation of chlorothalonil and the consequent accumulation of chlorothalonil and its toxic metabolite, 4-hydroxychlorothalonil, resulted from four successive applications at rates of 2, 4, and 10 kg a.i./ha. Soil respiration for 7 h (SR7) was slightly affected by chlorothalonil applications at all three levels, whereas soil respiration for 24 h (SR24) at 10 kg a.i./ha was reduced by 17.6-59.1 %, depending upon the frequency. This harmful effect of chlorothalonil on SR24 persisted throughout the experiment although it gradually weakened with time. A persistent inhibitory effect on soil dehydrogenase activity was also observed with repeated applications of chlorothalonil at 10 kg a.i./ha. This study indicated that repeated chlorothalonil applications may lead to the accumulation of chlorothalonil and its metabolite in soil under greenhouse conditions and thereby alter soil microbial activity.