Abstract: It was found that wheat leaves sprayed with aureomycin solution showed a higher rate of photosynthesis by 10%–31%. The chloroplasts isolated from aureomycin treated leaves also sustained a higher photophosphorylation activity in both cyclic and noncyclic reaction systems. In non-cyclic system, the enhancement of photophosphorylation is more than that of electron transfer thus resulting in a P/2e of 1.5, significanthy higher than that of ordinary chloroplast preparation which is considered as a unit. The relationship between the increase of P/2e ratio of the isolated chloroplasts and the promotion of photosynthetic rate by aureomycin was discussed.