The isocitrate dehydrogenase leaky mutant Alcaligenes eutrophus RM-1 was isolated after mutagenesis, and its metabolic characteristics were investigated. The PHB accumulation was significantly increased due to the increased how of carbon to the PNB biosynthetic pathway instead of the TCA cycle, due to the activation of PHB biosynthesis-related enzymes induced by the acetyl-CoA accumulated intracellularly. The PHB accumulation pattern changed from non-growth associated to growth associated. The effects of several cultivation conditions on PHB accumulation and cell growth were also investigated. The PHB accumulation in mutant strain A. eutrophus RM-1 proceeded more favorably at a higher C/N molar ratio and lower carbon concentration compared to that of the parent strain. In P(3HB-3HV) biosynthesis, the molar fractions of 3-hydroxyvalerate and 3-hydroxyvalerate yield per amount of propionate utilized were increased due to the increased conversion of propionate to 3-hydroxyvaleryl-CoA rather than to acetyl-CoA and CO2. Modification of the efficiency of the TCA cycle of A. eutrophus was found to be an effective method for increasing biosynthesis of PHB and its copolyester in the strain.