To produce polyhydroxyalkanoate (PHA) copolymer which consists of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx) by cultivation of Aeromonas hydrophila, fed-batch cultures were done under several nutrient limiting conditions. With the results from flask cultures, fed-batch cultures were carried out to produce large amounts of PHA. In the fed-batch culture, firstly glucose was fed to grow cell, and then, oleic acid fed to stimulate PHA in the cell. The final cell concentration, PHA content, PHA concentration, and 3-hydroxy-hexanoate fraction in 38 hr were 48.9 g/L, 15.05 wt%, 7.36 g/L and 12.2 wt%, respectively, resulting in the productivity of 0.19 g/L-h under phosphate-limiting condition.