BackgroundPhysical activity increases the performance of the nervous system by stimulating the body’s metabolism and improving the efficiency of the ATP production system.ObjectivesIn the present study, the effect of twenty minutes scuba diving in high depth (10m) on cognitive function and stress system activity was investigated.MethodsTwelve professional scuba divers with a mean age of 23 ± 1 year, weight of 80 ± 2.5 kg and height of 1.79 ± 3.5 cm resident in the city of Mashhad participated in the test. Their cognitive functions were measured 60 min before and 20 min after diving and the data were evaluated using the PASAT software. In the present study, parameters such as general mental health, sustained attention, average response speed, and mental fatigue were measured. Moreover, in order to determine the activity of the stress system, their salivary cortisol was collected before and after diving.ResultsResults revealed that, the general mental health of these scuba divers was normal and it did not undergo a remarkable change after diving. Their average response speed and sustained attention had a significant decrease after scuba diving. Mental fatigue after diving increased. Also, salivary cortisol level significantly increased after diving.ConclusionsAccording to our data, it seems that scuba diving as stress stimulant increases cortisol level and therefore reduces cognitive performance after diving.