Poly –hydroxyl butyrate( PHB) is a natural,biodegradable polymer accumulated in the form of intracellular granules by a large variety of bacteria. It is among the most investigated biodegradable polymer in recent years. The PHBs are non-toxic, biocompatible and biodegradable thermoplastics  that can be produced from renewable resources. The study aimed at screening and identifying a potential PHB accumulating B.megaterium PTCC 1656 and optimization of media parameters for increased PHB production by this strain bioplastics. For this study B.megaterium PTCC 1656 was purchased  from the fungi and bacteria collection center of the Iranian science and technology research organization. An their PHB production was determined under different conditions such as incubation time, Carbon and Nitrogen source. The result showed that , glucose was the best carbon source and in this conditions the maximum production of PHB was 0.42 g/l at 45h. PHB production starts in response to stress imposed on cell usually by nitrogen limitation,although in the presence of abundant carbon source. Actually PHB production was dependent on nutrient limitation.