Effect of dissolved oxygen (DO) on the biosynthesis of orange pigments in Monascus fermentation was investigated in this study. The orange pigments production of the w1 Xia strain in a 10L bioreactor under different DO levels obtained using different ventilatory volumes and stirring speeds were studied. And the optimized conditions were applied in a 50L bioreactor. The results showed that the changing trend of substrate consumption, pH, and DO was similar under different ventilatory volume conditions, but the color value of orange pigments increased along with the ventilatory volume augment. The stirring speed did not have significantly effects on the biomass and color value of orange pigments. Meanwhile, the orange pigments production in a 50L bioreactor was similar to that in a bioreactor. In conclusion, the higher ventilatory volume and adapted stirring speed were beneficial to the biomass and orange pigments production.