Soil microbial respiration and its entropy, as a sensitive indicator of soil nutrient variation, are usually used to evaluate the microbial carbon use efficiency and soil carbon concentration variation. In this present study, the effects of forest conversion on microbial carbon use efficiency was studied by comparing differences of soil microbial respiration rate, microbial biomass carbon, microbial entropy, and metabolic entropy between Castanopsis carlessi natural forest (NF) and Pinus massoniana Lamb. plantation (PM) and Cunninghamia lanceolata Lamb. Plantation (CL). The results showed that (1) the soil microbial respiration rate in 0-10 cm of PM was 32% higher than that of NF. The soil microbial respiration rate in 10-20 cm of PM and CL were 26% and 24% lower than those of NF, respectively (P<0.05). The microbial respiration rate in 20-40 cm and 40-60 cm soil layer of NF were 50% and 43% higher than that of PM. (2) Soil microbial biomass carbon (MBC) in 0-10 cm of PM and CL were 19% and 40% lower than those of NF, respectively (P<0.05). The MBC in 10-20 cm of PM was 29% higher than that of NF (P<0.05). (3) Soil microbial entropy in 0-10 cm of CL and PM were not significantly different from that in the natural forest. It decreased 51% and 71% in 20-40 cm, 52% and 66% in 40-60 cm (P<0.05). Effects of forest conversion on metabolic entropy could only be found in 0-10 cm soil layer but not subsurface layer. The metabolic entropy in PM and CL 38% and 29% higher than that of NF, respectively (P<0.05). In conclusion, the forest conversion decreased the soil microbial carbon use efficiency in the surface layer, the ratio of labile to total carbon pool in the surface layer, and availability of organic carbon.