High cell density culturing has been conducted for the production of poly(3-hydroxybutyrate) fed-batch cultures of Ralstonia eutropha with phosphate limitation. It was found that a high glucose concentration inhibited the synthesis of P(3HB) in the high cell density culture of R. eutropha. Although a low glucose concentration can trigger the synthesis of P(3HB) in a manner similar to that of phosphate limitation, it also limited both the P(3HB) synthesis and the cell growth, and led to a low P(3HB) productivity because glucose is the sole carbon source in this reaction. An unstructured model was proposed for predicting the cell growth and P(3HB) synthesis in high cell density cultures of R. eutropha, where the phosphate concentration played a key role in the accumulation of P(3HB) and in cell growth. Good agreements were found between the experimental data and model predictions. The results of simulation showed that the final P(3HB) concentration would decrease more than 25% when the glucose was concentration increased to 40 g/L, and indicated that the optimal glucose concentration for P(3HB) production by high cell density cultures of R. eutropha was around 9g/L.