Introduction: Epilepsy is one of the most common neurological disorders. In spite of the fact that a great development has been made regarding therapy against epilepsy, little is known, however, about the precise mechanism of the epilepsy. Pentylenetetrazol (PTZ) is one of the most often used epileptogenic agents. Hence the main purpose of the present work was to determine the effect of PTZ as a convulsant drug on the bioelectrical activity and neuronal excitability of D5 neurone in Helix aspersa. Materials and Methods: Experiments were carried out on D5 neuronal soma membrane located in the left parietal ganglion of snail, Helix aspersa. The properties of the action potentials were analyzed using two electrodes current clamp technique. Results: The results showed that the injection of 1 nA depolarizing current in the presence of PTZ caused an increase in the frequency and the duration of action potentials by about 11.7% and 14% respectively. It also led to a 32.3% decrease in the amplitude of afterhyperpolarization and the amplitude of action potential by about 2-3mV. Furthermore when PTZ (25 mM) was applied extracellularly, the resting membrane potential of the D5 cell became hyperpolarized by about 4 mV. Conclusion: These findings suggest that PTZ induces changes in bioelectrical properties which effect on neuronal signaling.