Abstract：Objective：To observe the curative effect of modified Dingxian Decoction in adjuvant therapy of grand mal seizure and its effect on interictal epileptiform activity(IEA) on electroencephalogram and oxidative stress. Methods： A total of 84 cases of patients with grand mal seizure were selected and randomly divided into the observation group and the control group according to the envelope method，with 43 and 41 cases in each group respectively. The control group was given conventional treatment，and the observation group was additionally treated with modified Dingxian Decoction based on the treatment of the control group. Clinical effects， IEA condition， and adverse reactions were compared between the two groups. The oxidative stress indexes including total antioxidant capacity(T- AOC)， glutathione peroxidase (GSH-Px) and malondialdehyde(MDA)，the Quality of Life in Epilepsy Inventory-31(QOLIE-31) Score，and the Montreal Cognitive Assessment(MOCA) Score were compared between the two groups before and after treatment. Results：The total effective rate was 88.37% in the observation group，higher than that of 70.73% in the control group(P＜0.05). After treatment， the IEA condition in the observation group was better than that in the control group，and the percentage of disappearance or decrease of IEA more than 50% in the observation group was 81.40% ， higher than that of 56.10% in the control group(P＜0.05). Before treatment，there was no significant difference being found in the comparison of levels of T-AOC， GSH-Px and MDA between the two groups(P＞0.05). After treatment，levels of T-AOC and GSH-Px in the two groups were increased when compared with those before treatment(P＜0.05)，and MDA levels were decreased(P＜0.05)； levels of T- AOC and GSH- Px in the observation group were higher(P＜0.05)， and MDA level was lower than those in the control group(P＜0.05). Before treatment，there was no significant difference being found in the comparison of scores of QOLTE-31 and MOCA between the two groups(P＞ 0.05). After treatment，scores of QOLIE-31 in the two groups were higher than those before treatment(P＜ 0.05)，and the score in the observation group was higher than that in the control group(P＜0.05). There was no significant difference being found in the comparison of the incidence of adverse reactions between the two groups(χ 2=0.611， P=0.435). Conclusion： Modified Dingxian Decoction in adjuvant therapy of grand mal seizure has a good effect and high safety，which can significantly improve IEA on electroencephalogram and oxidative stress indicators.