Abstract: The result of the experiment in switching photoperiods shows that photoperiod-sensitivity of millet plants spreads out chiefly before the differentiation of the shoot apex. A shift in leaf esterase isoenzymes during the early growth period is advanced by SD (8h) treatments, and delayed by LD (Cont Illum) treatments. The shift in isoenzyme may involve a change in differentiation-stage of young plants. LD treatments result in a gradual decrease of α-amylase activities in the early successive leaf layers of newly expanded. The α-amylase activity reaches its minimum at 6 leaf-stage, and thereafter appears to increase. But SD treatments can prevent the α-amylase activity level from the V patternfluctuation. Both the content of free ascorbic acid and the peroxidase activity in leaves show a fluctuation accopanying plant growth, and reach their minimum at 6 leaf-stage. Under SD (8h) the 6 leaf-stage coincides with the onset of elongation of shoot apex.