We measured CO₂ emission rate from pruning materials by in vitro incubation under the optimum condition for microbial activity and estimated percentages mineralizable carbon to total carbon (mineralizable C ％) of various pruning materials (different species and parts), using kinetic analysis. Depend on the species and parts, i.e. fine branches (diameter<10mm), thick branches (10mm<diameter<30mm), or trunk, mineralizable C ％ were changed from 2 to 41％. These differences were reflected the C / N ratio of the pruning materials. Mineralizable C ％ were less than 15％, 15～20％, more than 20％ correspond to the C/N>100, 30<C/N<100, C/N<30, respectively.