Soil ecosystems are complex and biogeochemistry of soils is governed largely by the functioning of soil biota community through their control over the biological pool of every elemental cycle. Biological pools of carbon (C), nitrogen (N) and phosphorus (P) in soils of hill rice ecosystems in North East India are not yet characterized. This study characterized an array of biological parameters of C, Nand P in soils of three common rice ecosystems viz. slope land, upland terrace and lowland. Soil samples (0-15 cm depth) were collected from six different sites located in two villages (Saiden and Kyrdemkulai) in post-summer and in postwinter seasons. The soil of each site differed significantly between seasons in terms of soil microbial biomass C, Nand P, total and dissolved organic carbon, extractable organic nitrogen, potentially mineralizable nitrogen, basal and substrate induced respiration, total Nand P, available Nand P, soil dehydrogenase and phosphatase activities (P < 0.01, n=20 as determined by paired t-test within a site) and these parameters were strongly influenced by soil moisture content. Pair-wise correlation matrix analysis revealed that biological parameters of C, Nand P were strongly influenced by each other (correlation coefficient r � : 0.36 at P<0.05, or � :0.46 at P<0.0I, n=30). Principal component analysis (PCA) performed season-wise considering the biological parameters as defined variables indicated that rice fields were grouped according to ecosystem type and soil moisture status, and such effects overrided the impacts of site differences in biological pools of C, N and P. Moisture content in soils observed to be a critical variable in hill rice ecosystems that control the size and dynamics of biological pools of C, N and P and the interrelationships among these parameters. Overall, it can be concluded that C and N components of soils in lowland and stabilized upland terrace rice ecosystems seem to be self-sustained, but the major limiting factor was availability of P.