This study investigated the impact of forest stand types and monthly variations on soil carbon fluxes (CO₂, CH₄), with a focus on soil microbial activity and key environmental drivers in the urban forests of Seoul, South Korea. From May to December 2024, CO₂ efflux and CH₄ uptake were measured using closed-static chambers once a month between 10 am and 2 pm in three urban forest stands: Prunus yedoensis (PY, deciduous broad-leaved), Pinus koraiensis (PK, evergreen coniferous) and Metasequoia glyptostroboides (MS, deciduous coniferous). Simultaneously, soil temperature (ST) and moisture (SM) were monitored. Additionally, topsoil at a depth of 0-10 cm was sampled to assess soil microbial biomass carbon (MBC) and nitrogen (MBN), and soil extracellular enzyme activities of β-glucosidase (BG), cellobiohydrolase (CBD), β-xylosidase (BX), and N-acetylglucosaminidase (NAG). The mean CO₂ efflux during the study period was 499 ± 71 mg C m^-² h^-¹ in PY, 296 ± 38 mg C m^-² h^-¹ in PK, and 229 ± 29 mg C m^-² h^-¹ in MS, respectively. CO₂ efflux was significantly influenced by both forest stand type and the sampling month (p < 0.001), with PY showing higher efflux than both PK and MS. Moreover, CO₂ efflux was highest in July across all forest stands (p < 0.001). The high ST in July enhanced soil microbial activity, as shown by the strongest positive correlation between CO₂ efflux and ST (R² = 0.87; p < 0.001) along with the strong positive correlations with MBC (R² = 0.73; p < 0.001), MBN (R² = 0.65; p < 0.01), BX (R² = 0.78; p < 0.001), CBD (R² = 0.86; p < 0.001), and BG (R² = 0.90; p < 0.001). Regarding CH₄, uptake was observed across all forest stands, with PY showing 40% greater uptake than PK, and 28.5% more than MS (p < 0.05). CH₄ uptake was significantly impacted by the sampling month (p < 0.001) and higher ST led to stronger CH₄ uptake (R² = 0.61; p < 0.001). Additionally, CH₄ uptake showed a moderate positive correlation with soil microbial activities (R² > 0.51; p < 0.05). Forest stands and sampling months significantly impacted carbon fluxes, with the greatest increase observed in PY in July, influenced mainly by the ST and microbial activities. Long-term monitoring is needed to determine how species-driven soil chemistry effects on carbon fluxes respond to seasonal and interannual climate variability.