In view of anxiolytic, antidepressant and memory strengthen properties of Allium cepa (AC; onion) bulb in various investigations; we aimed to evaluate the useful effects of onion on single immobilization stress -induced biochemical and behavioral changes. Mice in test group were treated with AC powder (200 mg/kg/day), dissolved in water, while the control group were received drinking water for 14 days. After 14 days control and AC treated mice were further divided into unstressed and stressed groups. Animals in the stressed group were subjected to immobilization stress for 2 h. 24-h after the immobilization stress, behavioral activities were monitored. Immobilization stress-induced an anxiogenic behavior in mice subjected to elevated plus maze test (EPM) and light dark activity test (LDA). 2-h immobilization stress-induced depressive behavior in animals measured by forced swim test (FST). Administration of AC attenuated the immobilization stress-induced behavioral deficits. Highest memory performance was observed in stressed mice that were pre-treated with AC in Morris water maze (MWM). Brain lipid peroxidation, antioxidant enzymes (SOD, CAT, GPx) and acetylcholinesterase (AChE) activities were also estimated. Present study suggests a role of antioxidant enzymes in the attenuation of 2-h stress induced anxiety and depression, and enhanced cognitive function as well by AC. The findings therefore suggest that supplementation of AC may be beneficial in the treatment of anxiety, depression and enhancement of memory function.