Abstract: Long-term effects of methylparathion contamination on soil microflora were investigated.Little difference in total counts of bacteria,actinomycetes and fungi was observed between the contaminated and the non-contaminated soil.Compared with the control,the contaminated soil was slightly lower in total count of azotobacters and denitrifying bacteria and significantly higher in those of ammonifying and ammonia-oxidizing and nitrifying bacteria.The respiratory intensity of the contaminated soil decreased by 29.93% while ammonification and nitrification increased significantly over that of control soil.The total DNA extracted from the contaminated soil and the control was （12.23±1.36）μg·g^-1 and （13.01±（1.91））μg·g^-1 dry soil,respectively.

Key words: methylparathion, long-term contamination, soil microorganism, ecological effect