Molecular biotechnology as one of culture-independent methods has been increasingly used in the studies of wastewater microorganisms, and many uncultured populations have been revealed, which have changed many views of microbial ecology. This paper gives a succinct review of recent studies in wastewater microorganisms. Some novel, in many cases yet not cultured bacteria were identified to be responsible for filamentous bulking and foaming as well as phosphorus and nitrogen removal in wastewater treatment systems ; however, some predominate population recognized previouslY were proved unimportant. The data give some insights about microbial diversity, population dynamics, terns stability and specific microbial population activity, and they will be helpful to optimize plant design and parameter control. ecosysprocess