A hypothesis on the role of the symbiotic fungi in fungus growing termites was examined on Macrotermes carbonarius, whose fungus comb had appearance different from those of other Macrotermes species reported so far. Chemical analyses of fungus comb of M. carbonarius indicated that decline of lignin concentration within the fungus comb, which has been observed in some Macrotermes species, was not observed, but the decrease was detected between the fungus combs. This new pattern of lignin degradation confirms the hypothesis that the role of the symbiotic fungi is to degrade lignin and improve cellulose digestibility.