Eco-friendly biopolymers, polyhydroxybutyrate, have been produced by many kinds of bacteria that possess most important applications in food packaging industries and also in medical field. In the present work, PHB production was economized through the statistical optimization of physical variables. The physical variables chosen for the enhanced production of PHB were incubation period, temperature, pH and inoculums size. The relative rate of production has been studied by understanding the complex interactions of variables using face-centred central composite design. The submerged fermentation with Acinetobacter nosocomialis RR20 produced PHB yield of 5.88 g/L at optimized conditions with a notable value change of sixfold increase in comparison with minimal salt medium and these findings have showed that the designed medium was significant in terms of higher of PHB production.