Polypyrrole/zeolite composites were studied as solid contact material in potassium ion-selective electrodes (K+-ISEs). Proton-exchanged Zeolite Socony Mobil-5 (H-ZSM-5) with SiO2/Al2O3 ratios of 23, 80 and 280 were electrochemically synthesized with polypyrrole (PPy). The anionic groups on the zeolite framework functioned as the counter ions for PPy during the reaction. H-ZSM-5 particles were observed on the surface as well as inside the composite films. PPy/H-ZSM-5 composites gave a similar cyclic voltammogram as PPy doped with chloride, PPy(Cl−). The hydrophobicity of the composites decreased in the order PPy/H-ZSM-5–23 > PPy/H-ZSM-5–80 > PPy/H-ZSM-5-280. The redox capacitance of the composite was better utilized than that of PPy(Cl−) after they were coated with a plasticized PVC membrane. PPy/H-ZSM-5 composite-based K+-ISEs exhibited similar potential stability as the PPy(Cl−)-based K+-ISE. However, when compared with the PPy(Cl−)-based K+-ISE, the detection limit of PPy/H-ZSM-5 composite-based K+-ISEs was enhanced after a long-term conditioning.