The experiments were carried out to produce PHB (Poly-β-Hydroxybutyrate) in activated sludge. The production of PHB under nitrogen limited condition was confirmed and CH3COONa was better than glucose as carbon source for production of PHB. Content of PHB was stabilized to its maximum stage around 250 hours by continuous process and it was achieved to 12% of dried sludge weight basis. PHB was slowly accumulated and consumption than carbohydrate in batch process.