A decline in the activity of Succinic dehydrogenase in rice grain was evident during progressive maturity of panicle in all the treatments of nitrogen i.e., N source and N dose as top dressing at 10 days before flowering (DG) with concomitant increase in panicle weight. The ammoniacal source of nitrogen as against nitrate nitrogen exhibited delayed progressive maturity of panicle resulting retention of higher Succinic dehydrogenase activity in grain and greater panicle weight tiller^-1. However, application of higher dose of nitrogen was more effective in maintaining greater Succinic dehydrogenase activity in grain resulting in increase panicle weight tiller-1 in both the early rice varieties.