Sildenafil is a phosphodiesterase-5 inhibitor and glutamate/nitric oxide/cGMP pathway appears to mediate memory enhancing effects. There are contradictory results about the effects of exercise and sildenafil on cognitive functions. Our aim was to investigate the effects of sildenafil pretreatment and chronic exercise on anxiety and cognitive functions. Wistar rats were divided into two major groups as sedentary and exercise. Moderate intensity swimming protocol was applied to the rats for 6 weeks, 5 days/week, 1 hour/day. Some of the rats were applied chronic sildenafil (25 mg/kg/day) at the last 2 weeks of exercise protocol and some of them were applied acute sildenafil (25 mg/kg), via orogastric route using ether as an anesthetic agent. For acute stress exposure, fresh cat feces and urine protocol was used at the end of exercise protocol and sildenafil pretreatments. The elevated plus maze test was used to evaluate the stress level and object recognition test was used for the cognitive functions. Decreased time spent in the open arms of the plus maze indicated increased anxiety levels, and the increased time spent with the novel object determined improved cognition. The rats were decapitated and the brain tissue was removed for determining myeloperoxidase (MPO), malondialdehyde (MDA), nitric oxide levels and lucigenin-enhanced chemiluminescence measurements. GraphPad Prism 5.0 was used for statistical analysis. ANOVA and student’s t test were used. The serum cortisol levels were risen following acute stress applications (p<0.05-0.001). In brain tissue increased MPO and MDA levels in sedentary-acute stress group (p<0.05) were decreased with acute or chronic sildenafil applications (p<0.05-0.001). Chronic exercise training inhibited the increase in MPO levels (p<001) and MDA levels were declined in acute or chronic sildenafil applied exercised rats (p<0.05-0.01). Nitric oxide levels were increased in acute stress applied sedentary rats (p<0.001) and diminished with chronic sildenafil pretreatment (p<0.01). Increased lucigenin chemiluminescence measurements, indicator of superoxide levels, were decreased in acute or chronic sildenafil pretreated sedentary rats (p<0.001). The time spent in the open arms of the plus maze was declined with acute stress application in sedentary rats (p<0.05) and increased back to control levels with chronic sildenafil pretreatment (p<0.001). In exercised rats acute sildenafil application prolonged the time spent in open arms compared to exercised group (p<0.01). The decreased time spent with the novel object in acute stress applied sedentary rats were increased with sildenafil treatment (p<0.05-0.01). The results of the study suggest that sildenafil pretreatment or exercise training might be protective in acute stress and improve cognitive function by decreasing oxidative damage parameters.