The effects of pH on the cell growth, the elaboration of pullulan, and the morphology of Aureobasidium pullulans IFO 4464 were examined. A. pulluans grew in yeast-like form at constant pH7.5 and in mycelial form at constant pH2.5. At the both pH conditions, the elaboration of pullulan was very low, about 6.0~6.5g/l. The mixture of yeast-like form and mycelial form of cells was found at the constant pH4.5, at which condition, the elaboration of pullulan was high, about 24.5g/l. The pH shift experimemts showed that the specific production rates of pullulan were 0.048($hr^{-1}$)for the mycelial form and 0.058($hr^{-1}$)for the yeast like form, which indicated that the yeast-like form has the similar, only slightly higher, biosynthetic activity of pullulan to the mycelial form at pH4.5 and the pH of culture broth is more important factor for the elaboration of pullulan than the morphology of A. pullulans.