In the present study, the effect of various light conditions on carotenoid accumulation in a novel heterotrophic microalga, Crypthecodinium sp.SUN was investigated. The results showed that C. sp. SUN mainly produced.carotene and beta-carotene. The total carotenoid content could reach to 12.8 mg g(-1) dry weight under high light intensity (100 mu mol m(-2) s(-1)), which was > 100-fold higher than that under dark condition. Besides, along with the light intensity increased, the ROS level in vivo was decreased at 48 h and 72 h. Further study showed that, light could efficiently promote the gene expression of PSY and LCYb, which explain the molecular mechanisms of carotenoids accumulation under light conditions. Meanwhile, slightly inhibited fatty acids accumulation could promote the carotenoids yield. The present work proposed that C. sp. SUN could be a potential carotenoid producer, and provided valuable insight for carotenoids biosynthesis.