The competence time of Streptomyces viridochromogenes for aerial mycelium formation was determined. Within 10 hrs after spore inoculation the submerged mycelium was programed to form aerial mycelium, when the former was laid on agar plate. The white aerial mycelium was formed 17-22 hrs after the transfer. Ascorbic acid oxidizing enzyme band on native gel showed chracteristic mobility change during aerial mycelium formation. Total activity of this enzyme did not show any correlation with the differentiation. The asay condition for the crude enzyme was determined. EDTA and $FeCl_{2}$ showed stimulatory effect. Approximate ratio of oxygen consumed to ascorbic acid oxidized was 1:1.