A new type of acetylcholine sensor was made with an Ion Sensitive Field Effect Transistor (ISFET) and acetylcholine receptor. The acetylcholine receptor was fixed on a polyvinylbutyral membrane which covered the ISFET gate. When acetylcholine was injected into this system, the differential gate output voltage gradually Shifted to the positive side and reached a constant value. This response was due to the positive charge of acetylcholine. A linear relationship was obtained between the initial rate of the differential gate output voltage change and the logarithmic value of the acetylcholine concentration. Acetylcholine was fixed in the range 0.1-10μM. When the acetylcholine receptor was immobilized with the lipid membrane, the response was amplified with both the positive charge of acetylcholine and sodium ion flux through the acetylcholine receptor's channel. Therefore, the difference in the differential voltage between the acetylcholine receptor-ISFET systems with and without the lipid membrane was caused by sodium ion flux through the acetylcholine receptor's channel.