Polyhydroxyalkanoates (PHA) are good candidates to plastics because of their complete biodegradability and material properties similar to petroleum derived plastics. They call be synthesized by numerous bacteria as intracellular carbon and energy storage compounds and accumulated as granules ill the cytoplasm of cells. Ill this Study, PHA storage capacity of activated sludge were tried to increase Under anaerobic/aerobic conditions and changing Microbial community in the SBR has been observed by combination of molecular techniques. Polyhydroxybutyrate fraction of the inoculum sludge which was 0.23% increased to 8.1% after 5 months operation of the SBR. Corresponding values were 0.04% and 2.45% respectively for polyhydroxyvalerate. Bacteroidetes species dominated the sludge sample taken from the SBR after 5 months of operation. by 28%. Bacteroidetes followed by Proteobacteria by 17%, and Actinobacteria by 15%.