A study was undertaken to study the response of submergence duration and age of the seedlings on enzyme activity like nitrate reductase and α-amylase. Leaf nitrate reductase activity of submergence tolerant rice genotypes like FR-13 A and TCA-85 was significantly higher than that of susceptible Pankaj and Mahsuri. Nitrate reductase activity declined under submergence in both tolerant and susceptible genotypes. A positive correlation was found between the nitrate reductase activity and survival (r²=0.74), which may be utilized as criteria of selecting the submergence tolerant genotypes for improving rainfed lowland rice growing ecosystem. Varieties with higher reductase activity had higher survival rate under submergence while α-amylase activity decreased under submergence. Maximum reduction in α-amylase activity was recorded in treatment with 11 days submergence.