Ten to 12 percent of the adult population globally suffers from migraine, which is the second most frequent type of primary headache, according to the American Academy of Neurology. Even though pain and attack-related impairment scored first, cognitive symptoms were the second most common. ; The current study intended to measure the latency of P300 wave during and after an acute attack of migraine among a group of patients known to have migraine in order to introduce an objective method to measure the cognitive function of migraineurs during migraine attack. ; This is a potential cohort study conducted at the neurological outpatient's clinics of Basra hospitals to the period from January until August 2021. The total number of subjects included in the study were forty-eight (48), thirty (30) patients and eighteen (18) age and gender matched control subjects. Patients were examined and selected by senior neurologist and diagnosed as having common migraine, then refereed to the neurophysiology clinic to perform cognitive function tests, for each patient two tests were done; first one during the acute migraine attack and second one after one month far ahead from the end of the migraine attack. In addition, one cognitive function test was done for the control group.; We discovered a highly important variance of the mean P300 latency of the patients during the acute attack of migraine as compared to the same group of the patients after repeating the exam one month far ahead from the end of the last migraine attack and one week ahead of being medication free. Also, we found the mean P300 latency of the patients during the acute attack of migraine is significantly higher than the mean P300 latency of the control subjects (P. value <0.00).; We found that all migraineurs in our study are having higher P300 latency values than control group during moderate migraine attack and this difference was significant which indicates that during moderate migraine attacks there is obvious impairment of cognitive performance abilities of those patients.