To study the seasonal variation and the influence factors of fluxes of greenhouse gas (CO₂, N₂O, and CH₄) emissions from the soils of a Eucalyptus urophylla×Eucalyptus grandis plantation and an Acacia mangium plantation, we conducted 1 year of continuous monitoring of the greenhouse gas fluxes from the two types of forest using a static chamber and gas chromatography. We found that the soil of both the E. urophylla×E. grandis plantation and the A. mangium plantation behaved as CO₂ and N₂O sources and CH₄ sinks. The N₂O emission fluxes from the A. mangium plantation soil were significantly higher (P < 0.01) than those from the E. urophylla×E. grandis plantation soil. There were no significant differences in the CO₂ emission fluxes and CH₄ uptake fluxes between the two forests. The seasonal patterns of greenhouse gas fluxes from the soils of the two types of forest were similar. The CO₂ emission fluxes from the soils of the two forests were single-peak curves, high in the rainy season and lower in the dry season. The uptake fluxes of CH₄ were single-peak curves, high in the dry season and lower in the rainy season. The N₂O emission fluxes were higher during the rainy season than during the dry season, with two peaks in the rainy season. The fluxes of CO₂ or N₂O from the soils had highly significant (P < 0.01) positive correlations with soil temperature at 5 cm depth. The fluxes of greenhouse gases (CO₂, N₂O, and CH₄) from the soils had highly significant (P < 0.01) or significant (P < 0.05) positive correlations with soil water content. The emissions of greenhouse gases from the soils of the E. urophylla×E. grandis plantation and the A. mangium plantation were 31.014 t/hm² and 28.782 t/hm², respectively, and were composed mainly of CO₂(98.46%-99.15%) with a small amount of N₂O and CH₄.