Abstract: A series of 2,4-diamino-6-N¹-(substitiited benzyl)-N²-(substituted methylidene)-hydrazino-quinazolines (Ⅱ) were prepared. These compounds were synthesized from 2,4-diamino-6-substituted benzylaminoquinazolines by nitrosation and reduction to give 2,4-diamino-6-N¹-(substituted benzyl)-hydrazino-quinazolines which were subsequently reacted with Substituted aldehydes to yield the corresponding compounds (Ⅱ).In preliminary screening tests on infected mice these compounds showed suppressive effect against Plasmodium berghei. In Plasmodium yoelii-Anopheles stephens system, 11 compounds showed causal prophylactic activity in varying degrees. 6 of them(Ⅱ_1,7,8,11,15, Ⅲ₁) protected the mice from being infected when administered at an oral dose of 2.5 mg/kg for 3 consecutive days.