Abstract: The effects of forced periodic oscillation of oxygen concentration on the propylene ammoxida-tion reaction over a Mo - Bi catalyst were investigated in a continuous flow micro - fixed bed reactor at 44℃. The propylene conversion, acrylonitrile selectivity and periodic average yield were studied with various forced oscillation patterns and compared with the results of steady - state operation , which is the condition of industrial operation. The results show that the periodic average yield of acrylonitrile under any forced periodic oscillation of oxygen concentration among this experimental conditions, thus obtained could higher than that under the steady - state condition. A better forced periodic oscillation condition was that the low ratio of oxygen with propylene 9.0, operation time 210 min, and the high ratio 10.5, operation time 60 min. Operating under this condition, the periodic average yield of acrylonitrile reached 80.70% , increased about 2.3% compared with the acrylonitrile yield of steady- state operation.