Abstract: The present investigation deals with 2,4-D dichlorophenoxy acetic acid(2,4 D)on the multiplication of Anabaena at batch culture in laboratory, mass culture of algae nursery bed in outdoor and large-scale culture in polyethene sheet canopy. Multiplication of Anabaena was treated with 2,4-D at the concentration range 0.01—2.00μg/mL, and the effects of stimulation in lower concentration is better than that of higher one.when the concentration of 2, 4-D is 0.01μg/mL, contents of protein and chlorophyll a increase. At the concentration of 0.05μg/mL, the contents of protein and chlorophyll a are similar to the control. But the contents of protein and chlorophyll a decline when the concentration of 2,4-D increase up to 0.1μg/mL. The present investigation suggests that concentration of 2,4-D used for multiplication of Anabaena should be less than 0.05μg/mL, the optimal concentration is 0.01μg/mL.