Abstract: Thermal metabolic activity and Cu²⁺ fixation/transformation ratio (Z) of microbes in paddy soil and marsh sediment from the Huixian Wetland, Central Guilin, under Cu²⁺ (800-4000 μg·g^-1 ) stress were investigated with the microcalorimetric method coupled with conventional analytic methods. Results show that under the stress of 800 μg·g^-1 Cu²⁺, Z of the microbes in the paddy soil and the sediment was 44.93% and 34.59%, respectively, however under the stress of 4000 μg·g^-1 Cu²⁺, it rose to 93.16% and 85.13%, respectively; the 50% inhibiting concentration of Cu²⁺ against the microbes thermal metabolism was 2043 μg·g^-1 in the paddy soil and 2325 μg·g^-1 in the marsh sediment; metabolic activity of the microbes was obviously lower in the paddy soil than in the the wetland sediment. Z of Cu²⁺ increased with Cu²⁺ concentration under the joint effect of the soil and its microbes. Under the same conditions, metabolic rates of the microbes in the paddy soil and in the marsh sediment were significantly correlated (P<0.05，P<0.01). All the above findings show that the role of soil microbes in Cu²⁺ fixed/transformed has obviously changed as wetlands are reclaimed into paddy soil, and can be used as scientific basis for management of the wetland resources in Guilin.