The electrical properties of the diaphragm muscle low and high temperatures have been studied at previous studies, but there is very little information in the literature as to what changes occur during temperature changes. Therefore, this experimental study was designed to investigate the effects of temperature changes on electrical properties of Wistar rat diaphragm muscle in vitro. Muscle strips were removed from the ventral-costal regions of rat diaphragm muscles, placed into the organ baths containing Krebs solution and recorded at 22, 25, 30, 35 and 37 degrees C. Parameters (depolarization time, half repolarization time, amplitude, overshoot, and latency) of action potential and resting membrane potential measured by using the conventional glass capillary electrodes at different temperatures. Though not significant, amplitude of resting membrane potential was observed to decrease when temperature was increased from 22 degrees C to 37 degrees C. Also, the significant decrements in parameters of action potential occurred with increasing temperature. Our results demonstrated that in rat diaphragm muscle, action potential parameters are temperature-sensitive because depolarization time, half repolarization time, amplitude, overshoot, and latency were significantly reduced with rising temperature.