This experiment was conducted to study the effects of vitamin D₃ supplemental level on growth performance and immune function of Monopterus albus. A total of 540 healthy M. albus with an average body weight of (21.7±2.1) g was randomly assigned to 6 groups with 3 replicates per group and 30 M. albus per replicate. The M. albus in the 6 groups were fed with the basal diet supplemented with 0 (control group), 250, 500, 1 000, 2 000 and 4 000 IU/kg vitamin D₃, respectively. After 90 days feeding, researchers randomly selected 6 M. albus in each group, and drew blood from caudal vein to detect the related immune indexes of peripheral blood after growth performance determination. Furthermore, researchers injected Aeromonas hydrophila into 20 M. albus randomly selected in each group to observe the cumulative mortality of the M. albus challenged with A. hydrophila. The results showed as follows: compared with the control group, except 4 000 IU/kg group, the weight gain rate and protein efficiency ratio in other groups were significantly improved (P<0.05), and feed conversion ratio was significantly decreased (P<0.05); in 500 and 1 000 IU/kg groups, the levels of immunoglobulin M, complement 3 and complement 4, the activity of lysozyme, and the amounts of CD3, CD4 and CD8 of T cells with CD4/CD8 in serum were increased significantly (P<0.05), in addition the number of whole blood leukocyte, neutrophil, intermediate cell and lymphocyte was significantly increased (P<0.05), moreover, the cumulative mortality of the M. albus challenged with A. hydrophila was obviously decreased. No significant differences were found in all indexes except serum immunoglobulin M level between 4 000 IU/kg group and control group (P>0.05). In conclusion, supplementation of appropriate (500 and 1 000 IU/kg) vitamin D₃ can enhance humoral immunity, cellular immunity and nonspecific immunity function of M. albus, thus improving the resistance ability to pathogenic bacterium; moreover, lack or excessive supplementation of vitamin D₃ can result in the lower immune function of M. albus.