Soil nitrogen (N) is one of essential nutrients limiting primary productivity and reproduction in temperate forests. Root exudates is hypothesized to stimulate microbial activities and facilitate N release from rhizosphere soil, while another hypothesis exists that root exudation increases microbial growth and N competition between plants and soil microbes. The relative importance of two processes in microbial growth and N mineralization activities are assessed in beech forest soil in Mt. Naeba. We tested whether microbial biomass and N mineralization activities are greater in rhizosphere soil, compared to bulk soil during growth season. We measured root exudation between organic and mineral soil horizons, microbial biomass C and Nusing chloroform-extraction method, soil extractable C and N, and microbial proteases and arginase activities using casein and arginine assays, respectively. Both root exudation C and microbial biomass increased in summer, but rhizosphere effects are not detected. Protease activities increased in autumn, while arginase activities increased in latter stage of growth season to winter, consistent with decrease in tree and microbial N demand and accumulation of inorganic N during winter. Microbial biomass and associated N demand depends on temperature or soluble C availability, while microbial N mineralization is also affected by tree and microbial phenology.