The accumulation of poly(3-hydroxybutyric acid) in activated sludge was investigated. Fed-batch culture was carried out using sodium acetate as the source of carbon. A lack of nitrogen was a stimulating factor of accumulation P(3HB). Two experimental series were run. In series 1, nitrogen was fed into abacterial culture once for the first 24 hours, in series 2 ? for 6 hours each day of the experiment. The effect of operational conditions was evaluated based on the accumulation of P(3HB) in biomass, specific growth rate of microorganisms (m) yield coefficients (YP(3HB)/C, YP(3HB)/X), and productivity P(3HB). It was proved that the degree of accumulation of P(3HB) in activated sludge was comparable in both series. The highest P(3HB) yield of 0.59 g P(3HB)/g COD was attained in series 1 at the 12 th our after ceasing the nitrogen feeding. In series 1, between the 36 th and 48 th hour, the productivity reached the level of about 34 mg P(3HB)/l?h). In series 2, YP(3HB)/C and the productivity accounted for 0.21 g P(3HB)/g ChZT and 21.58 mg P(3HB)/l?h, respectively. The limiting factor of P(3HB) productivity was low specific growth rate of microorganisms of activated sludge. The maximum specific growth (max) reached 0.03 h-1 in series 1 and 0.022h-1 in series 2.