In order to determine sleep disorders, especially insomnia due to exam stress in medical students, moreover are there any bad effects on performance of mental abilities and emotional competency, we carried out this research. We used Prospective cohort study design, involving III and IV grade 60 students, once these grades are most overloaded courses. The study performed through 2 stages: 1) Just after Final examination of a block, 2) During regular days, after sleeping well. The aim can be divided into three main categories, including evaluation of sleep disorders, estimation of brain performances and emotional competency. An average sleeping time was 3.67±1.45 hours on final exam day, whereas a main sleeping time during regular day was 7.88±1.19 hours. As totally 70% of students were estimated as having insomnia and according to insomnia severity index, 58.3% of them had subthreshold insomnia, 16.7% of them had moderate insomnia. Furthermore, regarding to Epworth sleepiness scale, 36.7% of all participants were evaluated as having mild daytime sleepiness, 13.3% had moderate, and 10% had severe sleepiness, which was more common in male students. The estimation of emotional competency consists of self-awareness, managing emotions, motivating oneself, empathy, and social skill, which were strongly associated with duration of sleep time, as well as, emotion was more stable in 4th grade students. As comparison between mental performances of sufficient and insufficient sleep time, main difference of speed 3428±1249, memory 2984±1063, attention 2472±31, flexibility 4525±1184, and problem solving 945±193 scores.