Termites are a highly uncertain component in the global source budgets of CH 4 and CO 2. Large seasonal variations in termite mound fluxes of CH 4 and CO 2 have been reported in tropical savannas but the reason for this is largely unknown. This paper investigated the processes that govern these seasonal variations in CH 4 and CO 2 fluxes from the mounds of Microcerotermes nervosus Hill (Termitidae), a common termite species in Australian tropical savannas. Fluxes of CH 4 and CO 2 of termite mounds were 3. 5-fold greater in the wet season as compared to the dry season and were a direct function of termite biomass. Termite biomass in mound samples was tenfold greater in the wet season compared to the dry season. When expressed per unit termite biomass, termite fluxes were only 1. 2 (CH 4) and 1. 4 (CO 2)-fold greater in the wet season as compared to the dry season and could not explain the large seasonal variations in mound fluxes of CH 4 and CO 2. Seasonal variation in both gas diffusivity through mound walls and CH 4 oxidation by mound material was negligible. These results highlight for the first time that seasonal termite population dynamics are the main driver for the observed seasonal differences in mound fluxes of CH 4 and CO 2. These findings highlight the need to combine measurements of gas fluxes from termite mounds with detailed studies of termite population dynamics to reduce the uncertainty in quantifying seasonal variations in termite mound fluxes of CH 4 and CO 2.