Penicillin sensor was prepared by immobilizing penicillinase (Pcase) on $H^{+}$-selective carboxylated poly (vinyl chloride) (PVC-COOH) membrane or cellulose filter membrane. The immobilization techniques are as follows. Pcase was immobilized with GTH on $H^{+}$-selective PVC-COOH membrane or some amount of BSA was dropped on that membrane. Another method to make immobilization is to mix type I Pcase with GTH and drop on a cellulose filter membrane. According to immobilization techniques, there were some differences in response properties of enzyme electrodes, however, all electrodes responded to Pcase-resistant penicillin derivatives. Pcase immobilized on cellulose filter membrane with $H^{+}$-selective PVC membrane eletrode was more stable and more sensitive to penicillinase-resistant penicillin derivatives than any other immobilization techniques.