Previously, permeability of partly crosslinked poly( acrylic acid)-poly(ethy1enimine) complex capsule membranes has been shown to be controlled responding to external pH [K. Kono, F. Tabata, and T. Takagishi, J. Membr. Sci., 76, 233 (1993)l. In order to improve pHdependent permeation behavior of the polyelectrolyte complex capsule membranes, poly(methacry1ic acid), which has hydrophobic side groups, was used as a polyanion component instead of poly(acry1ic acid). The polyelectrolyte complex capsules composed of poly(methacry1ic acid)-poly(ethy1enimine) with a diameter of 5.2 mm were prepared. Permeation of phenylethylene glycol, which was used as a permeant, through the capsule membrane was quite limited at pH between 4 and 8. The permeation of the permeant across the capsule membrane in these pH regions was much less than that of poly(acry1ic acid)poly(ethy1enimine) complex capsule membrane. However, the permeability constant was drastically increased in the order of 1 or 2 above pH 8 and below pH 4, depending on temperature. The Arrhenius plot for the permeation of phenylethylene glycol through the capsule membrane showed that the activation energy for the permeation is almost constant in the pH region between 4.5 and 8, but greatly decreases below pH 4 and above pH 8.8, suggesting occurrence of a significant change of the capsule membrane structure near these pH regions due to dissociation of polyelectrolyte complex. When environmental pH of the capsule was changed, release rate of phenylethylene glycol from the capsule was altered quickly and reversibly under acidic condition.