Microbial degradation of metsulfuron-methyl by selective Penicillium sp.was studied.The results were shown as follows: During the degradation of various forms of ¹⁴C-metsulfuron-methyl in soil,the effect of Penicillium sp.was not obvious to degradation of extractable metsulfuron-methyl,but the effect was very clear to degradation and mineralization of bound residues of metsulfuron-methyl and mineralized metsulfuron-methyl.On bound residues of metsulfuron-methyl,Penicillium sp.selected made the decrease concentration of loose combined metsulfuron-methyl especially to the fulvic acid in it.But organic manure might increase the concentration of loose combined metsulfuron-methyl in some degree.