Soybean seed ageing during storage is one of the major causes of seed deterioration. Seed priming is an effective technique to improve seed quality of various crops. This study was undertaken to examine changes in mechanisms involved in stored seeds following priming. The seeds of vegetative soybean cultivar AGS-190 were harvested at harvest maturity and stored at room temperature (25ºC). The seeds stored for 6, 9 and 12months were primed with water, 0.5% chitosan or-0.8 MPa PEG. The results indicated that prolonged storage of the seeds under room temperature reduced seed germination performance. The activities of catalase (CAT) and superoxide dismutase (SOD) decreased and accumulation of malondialdehyde (MDA) content and chromosomal damage increased with longer storage period. Seed priming with-0.8 MPa PEG improved the quality of 6 months stored seeds resulting in better germination percentage and germination index. Increase in SOD, CAT activities and decrease in the content of MDA and chromosomal aberrations were observed when 6 months stored seeds were primed with-0.8 MPa PEG. The study indicates that loss of seed germination during storage is related to failure of CAT and SOD enzymes to protect reactive oxygen species (ROS) attack which resulted in auto-oxidation of lipid and nucleic acid. The results here also suggest that improvement of stored seed quality following priming is associated with reduction of lipid peroxidation and genetic damage through increase stimulation of antioxidants enzyme systems.