A study was carried out to investigate the effects of the two acetanilide herbicides alachlor and metolachlor on microbial activities in sandy loam soil. Effects of the herbicides on C07 evolution were monitored for 50 d in ambient conditions. The results showed that alachlor and metolachlor generally caused an initial decrease in C07 release, which subsequently increased to control level after 25 d of incubation. Both herbicides exert less effect on C07 evolution at lower concentrations. Fungal and bacterial populations in the soil also declined in the presence of either herbicide at higher concentrations. Phosphatase activity was generally affected in the presenceOf either herbicide except in soil treated with metolachlor at 20 ppm