It was shown that different groups of wood decaying fungi have the same efficiency of oxidative conversion of organic carbon of wood debris to CO2: ratio of CO2/O2 for polyporoid fungi is 0.82, agaricoid − 0.79, corticioid − 0.77 and heterobasidioid − 0.88. Polyporoid and corticioid fungi significantly differ in carbon conversion activity: 3.6 ± 0.25 and 2.0 ± 0.19 mg CO2/dm2 hour-1 respectively. The both groups of fungi have in 1.5–1.9 times lower carbon conversion activity on coniferous wood than on deciduous. White rot fungi have higher (4.1±0.3 mg CO2 / dm2 hour-1) activity than brown rot fungi (3.0±0.32 mg CO2 / dm2 hour-1).