Objective  To study the characteristics of electrocorticography (ECOG) in patients with supratentoriumoccupying lesion but no epileptic seizures and the effects of heat coagulation of cortical transverse fibers on postoperative epilepsy.    Methods  Patients with supratentoriumoccupying lesion but no preoperative epileptic seizures were divided into treatment group (n=76) and control group (n=100). Patients in treatment group underwent resection of the lesion and heat coagulation of its surrounding tissues during which ECOG was performed to monitor their conditions. Patients in control group underwent simple resection of the lesion without heat coagulation of its surrounding tissues. The patients were followed up for 24-48 months (mean 33.6 months) after operation to compare the incidence of epilepsy between the two groups.   Results  ECOG displayed epileptic discharge in 65 patients (85.52%) of the treatment group. After heat coagulation

epileptic discharge decreased or disappeared in 41 out of the 65 patients with epileptic discharge. Early postoperative epilepsy occurred in 10 (13.5%）and 28 (28.00%) patients of the treatment and control groups

respectively (Chisquare=5.78，P＜0.05). Late postoperative epilepsy occurred in 11.84% and 27.70% of patients in the two groups

respectively (Chisquare=6.34，P＜0.05).   Conclusion  The positive discharge rate is rather high in patients with supratentoriumoccupying lesion but no preoperative epileptic seizures. The incidence of epilepsy is lower after removal of the lesion in combination with heat coagulation of its surrounding tissues than that after simple resection of the lesion.