Introduction: This study was designed to investigate the chronic effects of Formononetin on behavior; cognitive function and oxidative stress in mice. Materials and Methods: Male albino mice of either sex (25 – 30 gm) were used in the study. The mice were divided into six different groups (n=6). Group 1: Control group received water. Group II: Mice received 5mg/kg/day, p.o. Formononetin for 21 days. Group III: Mice received 20mg/kg/day, p.o. Formononetin for 21 days. Group IV: Mice received 50mg/kg/day, p.o. Formononetin for 21 days. Group V: Mice received Diazepam 1mg/kg/day, I.P. Group VI: Mice received Imipramine 10mg/kg/day, p.o. Group VII: Mice received Piracetam 75mg/kg/day, I.P. Result: Chronic administration of FMNT at dose ranges between (5, 20,50mg/kg/day) revealed that significantly increased the time spent in open arm and decrease the no of entries in close arm in EPM showed Anxiolytic effect and also decreased the no of entries in dark compartment and increases the time spent in light compartment and also shows locomotor activity by increased no of square crossing in OF, whereas Antidepressant activity found by decreased immobility time in TST and FST and also find out the learning memory by NOR test which significantly express neuroprotective behaviour. The antioxidant parameters such as SOD, GSH and CAT level was found to be significantly increased in the FMNT as compared to the vehicle control groups. Level of SOD was found to be more in high dose of FMNT (50 mg/kg/ day). Conclusion: Our results suggest that chronic administration of FMNT can be observed and evaluated in laboratory mice. FMNT treated mice shown the anxiolytic, antidepressant and neuroprotective behavior such as increased time spent in open area, increased time spent in light area, decrease in immobility and improvement in memory. Improvement in memory is due to FMNT neuroprotective activity.