To clarify soil respiration (soil CO 2 efflux, R s ) characteristics in a subtropical evergreen broad-leaved natural forest in Yambaru, Okinawa, Japan, we examined spatiotemporal variation in R s and its determining factors. We then compared yearly R s with the value in other forests. The spatial variation in R s (coefficient of variation [CV] = 38.9%) was not significantly related to temperature or soil water content but was evidently dependent on ground surface litter coverage. R s was greater in summer (ca. 7-10 μmol m À2 s À1 ), and its seasonal variation was exponentially related to soil temperature (Q 10 = 2.16). As a function of soil temperature, we estimated a yearly mean stand-scale R s of 5.17 μmol m À2 s À1 , and a total carbon efflux from the soil of 1959 g C m À2 year À1 for 2014. Despite showing similar seasonal patterns as those in temporal forests, the R s in this ecosystem is very high throughout the year, and the yearly value is much higher for natural mature forests. A mass balance approach suggests that the large amount of belowground carbon allocation of plants contributed to the high CO 2 emissions from the soils.