Chronic hepatitis B (CHB) is a common chronic disease. Previous studies have shown a link between 25-hydroxyvitamin D3 (vitamin D3) concentration and liver disease. Hepatitis B virus (HBV) infection has been attributed to the inappropriate functioning of cell-mediated immunity. However, the effects of vitamin D3, immune cell, and HBeAg status on HBV viral load in CHB patients are still unclear. We investigated the relationship between the serum concentration of vitamin D3, percentage of immune cells in peripheral blood, and the HBV viral load of CHB patients. Sixty CHB patients were recruited, and their blood samples were collected and analyzed. Vitamin D level was measured using a chemiluminescence assay. A level of 30 ng/mL or above was defined as a vitamin D3 sufficiency. We assigned vitamin D3 status as either normal (≥30 ng/mL), insufficient (20-30 ng/mL), or deficient (<20 ng/mL). T-lymphocyte and B-lymphocyte surface markers in peripheral blood were detected using flow cytometry. The factors associated with HBV viral load were analyzed using univariate and multivariate-adjusted models. The mean serum vitamin D3 concentration in the subjects was 20.9±5.6 ng/mL. Up to 88.3% of the patients were either deficient in or had insufficient vitamin D3. The gender, BMI, hepatitis B surface antigen levels, and ALT levels were significantly related to serum vitamin D3 levels. Serum vitamin D3 concentration, HBe status, HBs levels, ALT, and AST levels showed a statistically significant correlation with the HBV DNA levels. Serum vitamin D3 concentrations and hepatitis B surface antigen levels were strongly correlated with HBV DNA levels. Vitamin D3 levels were significantly associated with CD19 numbers (ß:-6.2, 95% CI: -10.5). In multivariate analysis, vitamin D3 levels in the deficient and insufficient groups, and the CD8, HBeAg, and WBC counts were significantly associated with HBV DNA levels. In the immune tolerance phase of HBeAg-negative chronic HBV infection, vitamin D3 may be a modulator of immune function via CD8, CD19, and HBV DNA.