The metabolism of monosaccharides by Wautersia eutropha and the hydrolysis of sucrose by invertase were simultaneously carried out to accumulate poly (3-hydroxybutyrate) (PHB) in batch fermentation. Sucrose is not directly metabolized by W. eutropha, but monosaccharides such as glucose and fructose hydrolyzed from sucrose are known as carbon sources for W. eutropha. The regulation of hydrolysis rate makes it possible to control the feeding rate. In other words, the monosaccharides can be gradually supplied by controlling the hydrolysis rate of sucrose. When the time to be completely hydrolyzed from sucrose to monosaccharides was adjusted to 24 hrs, the maximum PHB content was taken by fermentation for 24 hrs. This suggests that the relation between the hydrolysis rate of sucrose and the accumulation rate of PHB is important to obtain a high yield of PHB. When the hydrolysis rate of sucrose was fast by adding large amount of invertase, the growth of cells was preferred rather than the accumulation of PHB.   This result was unexpected because the cultivation was carried out under nitrogen free condition. Perhaps the invertase would be metabolized for the growth of cells because of peptide bond including nitrogen atom. Therefore a small amount of invertase is better for accumulating PHB. It was concluded that the regulation of hydrolysis rate of sucrose is an important factor to get the high yield of PHB.