Using magnetoencephalography (MEG), auditory evoked magnetic N100m were measured in patients with focal epilepsy and the influence of focal interictal epileptic spikes on primary auditory cortex (PAC) was evaluated. Spontaneous cerebral magnetic fields and auditory evoked magnetic fields were recorded in 40 epileptic patients and 9 healthy volunteers using MEG and latency of N100m in the bilateral hemisphere, and the distribution of epileptic spike dipoles were measured. Depending on the presence of structural lesions and the localization of spike dipoles, the patients were divided into groups as follows: group I, patients with structural lesions in PAC; group II, patients without structural lesions and with spike dipoles in PAC; and group III, patients with neither structural lesions nor spike dipoles in PAC. Nine healthy volunteers were recruited and evaluated as control group. Compared with group III and the control group, N100m latencies in groups I and II were significantly delayed. A delay in N100m latency was found not only among patients with structural lesions in PAC, but also among patients demonstrating cluster of epileptic spike dipoles in PAC. This finding indicates that the presence of epileptic spikes may influence the mechanism of processing auditory information in PAC.