Moringa  oleifera is a tropical plant, with great economic importance for food and medical industry; coagulant properties of seed proteins have been used to water treatment. Biologically active molecules have been isolated from seeds; proteins with erythrocyte agglutination properties (lectins) and embryotoxicity activity were already detected in seeds. The aim of this work was to evaluate in water treated with M. oleifera seeds (MoW), hemagglutinating activity (HA) and effect on Aedes aegypti larval development. The water was treated using 3 (MoW 1), 6 (MoW 2) and 15 (MoW 3) seeds/l. HA of MoW treatments was evaluated with human (types A, O and AB) and rabbit erythrocytes using microtiter plates; titer was defined as the lowest sample concentration which showed hemagglutination. Biological assays were performed (triplicates) according to methodology described by World Health Organization, with adaptation for recipients containing 20 ml of sample treatments, using A. aegypti larvae (20) in the first stage of development (L1); control corresponded to water without seeds. Larval development was observed after 0, 24, 48 and 72 h of incubation. Embryotoxicity was detected by alterations in larval development. MoW 1, MoW 2 and MoW 3, contained, respectively, 0.59, 1.86 and 3.89 mg/ml of protein, showing activity (titer of 2,048^-1) with human and rabbit erythrocytes. Treatment differences were detected on larval development. MoW 1 mantained 85% of larvae in L2 stage of development after 72  h of incubation. Larvae in L3 stage were observed with MoW 2 (35%) and MoW 3 (5%). Larval L4 stage was only detected in control. In conclusion, water treated with M. oleifera seeds contains lectin and interferes in A. aegypti larval development.