The aim of this work was to study the activity level of alkaline and acid phosphatases during the composting of green wastes and sewage sludge and to determine relationships between biotic and abiotic properties of compost and phosphatase activities. This study has revealed a noticeable separation of phosphomonoesterase activities into two distinct phases during composting. Alkaline and acid phosphatase activities were high during the first month of composting and then declined up to the end of the process. Both phosphatase activities were significantly correlated with a group of variables which are clearly related to advancement of maturity during the composting process: C/N, respiration, cellulase, protease, phenoloxidase activities, HA and Global Index of Composting Evolution (GICE) resulting from 14 biological and chemical parameters. This study has also revealed the complexity of factors regulating turnover of P in compost process since phosphatase activities appeared constrained across two thresholds: 60/70 and 100 microg of inorganic P g(-1) DM for activation and repression, respectively.