The optimization of poly-β-hydroxybutyrate (PHB) fermentation process is essential to obtain a high PHB productivity. An optimization of two-stage continuous culture system by complex method for PHB production is presented. PHB production rate of the system obtained in the present study was chosen as the objective function. The PHB production rate of the system was higher than that of the phasewise optimization method which maximizes the growth rate of residual biomass in the first stage and the PHB production rate in the second stage. When the inlet glucose concentration in the first stage increased, PHB content and yield also increased. When the fermentor volume ratio (V₂/V₁) was 0.5, maximum PHB productivity in the second stage was 2.86g/L ^.h, which is highest compared with the reported value on PHB.