Cumulative oxidation of cellular macromolecules during storage reduces seed longevity. This study was undertaken to unravel the physiological and biochemical changes in rice seeds that contribute to deterioration during storage. Rice seeds maintained at three different seed moisture contents (SMC; 10, 12 and 14%) were stored in airtight glass jars. Half of the jars were flushed with nitrogen gas to provide modified oxygen conditions, while the other half were sealed with natural air (21% O2). Seed quality in terms of germination and antioxidant defence mechanisms was monitored after 3 and 6 months of storage at 25°C. The results showed that seeds performed better when stored at low SMC (10 and 12%), whereas the deterioration process accelerated in seeds stored at higher SMC (14%). Coupling high SMC with the availability of oxygen in the storage environment produced a negative effect on seed quality and longevity. Results from the antioxidant analysis showed more activity in seeds stored with oxygen at high SMC (14%) compared to lower SMC stored in modified oxygen conditions. Therefore, it is recommended that storage with low moisture levels (12%) or below (10%) is the best to preserve rice seed quality. However, at higher moisture levels (14%), the availability of oxygen in storage is more harmful to seed lifespan and quality.