The present study has been conducted to evaluate the antialgal activities of the leaves crude extracts of Dodonaea viscosa plant. The antialgal activities of ethanol (80%) and diethyl ether crude leaf extracts of D. viscosa were tested against Microcystis flos- aquae, Scenedsmus dimorphus and Mougeotia scalaris. The agar well diffusion method was used to evaluate the inhibitory actions of these extracts with three concentrations: 5,10, and 20 mg/ml. The results showed that the ethanol extracts were more effective on algae than diethyl ether extracts. The alga: Mougeotia scalaris and Microcystis flos- aquae have more sensitive than Scenedsmus dimorphus to attack by the ethanolic extracts, while Mougeotia scalaris have more resistsnce to attack by the diethyl ether extracts followed by Microcystis flos- aquae, while Scenedsmus dimorphus have more sensitive to attack by diethyl ether extracts.