Gradient magnetic field topography (GMFT) with magnetoencephalography (MEG) has been developed to demonstrate magnetic-field gradients of epileptic spikes on a volume-rendered brain surface. We evaluated GMFT in patients with anterior 2/3 corpus callosotomy (ACC) for drop-attacks. METHODS: Eight patients (age; 11-37 years) underwent ACC. GMFT evaluated the predominant distributions (anterior/posterior) and the spreading patterns (unilateral/bilateral) of pre- and postoperative interictal MEG spikes corresponding to generalized spikes on EEG. We compared the occurrence of four types of spikes; anterior unilateral spike (AUS), posterior unilateral spike (PUS), anterior bilateral spike (ABS), posterior bilateral spike (PBS) between 5 patients (group G) with good control of drop attacks and 3 patients (group P) with residual drop attacks. RESULTS: Preoperatively, GMFT showed the proportion of ABS in group G (mean ± SD, 57.4 ± 9.7%) was significantly (p=0.024) higher than that in group P (31.6 ± 15.2%). The number and proportion of postoperative ABS and PBS in group G were significantly decreased (p<0.05 in all). CONCLUSION: GMFT is valuable to evaluate pre- and post-operative predominant spikes in patients with drop attacks. SIGNIFICANCE: GMFT revealed a higher proportion of preoperative ABS and postoperative decline of both ABS and PBS in patients with good control of drop attacks after ACC ¹⁾.