PURPOSE: Cyclosporin is used in children with immune-mediated diseases, chronic disease, organ transplantation, or malignancy. These diseases often require a higher dose of cyclosporin, and cyclosporin displayed neurotoxicity of the central nervous system (CNS) neurotoxicity. Especially, cyclosporin-induced seizures often represent a physical threat to patients. And, the adverse effects of cyclosporin on CNS are considered. METHODS: The study was done with Sprague-Dawley rats(14-21 days), weighting from 28.7 g to 49.2 g. The animal were kept in-groups with mother rat in cages, and had free access to food and tap water. The temperature of the animal room is room temperature. Hippocampal slices were taken. Hippocampal slices were exposed to cyclosporin dissolved by 0.1% DMSO(Dimethyl sulfoxide). Then, we began to record electrical activity of slices every 10 minutes in low calcium environment. We observed the frequency and duration of electrical activity. RESULTS: The mean duration and frequency of cyclosporin 3M-treated ictal activity was 35.51.4 seconds and 133.017.9. These results were significantly different compared to the control group. The mean duration and frequency in cyclosporin 3M-treated interictal activity was 116.444.4 seconds, 63.635.8. There were no significant differences in the duration and frequency of onset in cyclosporin 3M-treated interictal activity compared with control showing interictal activity. The mean duration of latency time of onset in cyclosporin 3M-treated interictal activity was 166.229.8 seconds(n=9), and there was a significant difference in the latency of onset time in cyclosporin 3M-treated interictal activity compared with control showing interictal activity. CONCLUSION: Although cyclosporin neurotoxicity is well recognized, and the exact mechanism of cyclosporin neurotoxicity is still unclear, cyclosporin neurotoxicity is present under hypocalcemia. And, our results suggest that careful usage of cyclosporin in clinical conditions with hypocalcemia is required to avoid cyclosporin neurotoxicity.