The effects of Cd, As and Pb added to paddy soil on microbes in soils were assayed in pot experiment. Values of ED₃₀ fungi, actinomycetes, bacteria and nitrifiers were estimated. The texicity of the three elements on microorganisms in soils tested is in the order of As>Cd>Pb.In pot experiment, the luminescence of Plzotoziacterium phosphoreum spp. T₃ showed strongly negative relation to the concentration of the three elements. In field investigation, it is also strongly negatively related to the concexttration of Cd, but moderately related to that of As and Pb.It was defined by pot experiment that luminescence "100%" and "80%" of the strain T₃ could be regarded as critical luminescence of two grades, and so the critical concentrations of metals added to the potted paddy soil corresponded with it was estimated.