The influence of manure, chemical fertilizers, heavy metals and cleaner on the rate of degradation of alachlor in soil was studied. The degradation rate of alachlor in the soil followed first-order reaction kinetics. The half-life was 6.4 days. The degradation was accelerated by the amendment of manure. Adding chemical fertilizers to the soil enhanced alachlor degradation more in the presence of nitrogen than potassium. On the other hand, adding heavy metals or cleaner to the soil decreased the degradation rate. The half-life of alachlor in soil treated with Cd, Cr, Ni, Zn and Cu was 11.0, 8.3, 7.9, 7.2 and 6.7 days, respectively, and that of the cleaner is 7.5 days. The microbial biomass and the respiration rate in the soil were promoted by the amendment of manure and chemical fertilizers, and inhibited by the addition of heavy metals and cleaner. The degradation rate correlate positively with the microbial biomass and the respiration rate.