BACKGROUND: The carcinogen dimethylbenzanthracene (DMBA) is immunotoxic. Thymoquinone, meanwhile, is known to have antioxidant and anti-inflammatory effects. AIM: This study aims to determine the effect of thymoquinone and tamoxifen on the CD4CD25Treg count in Sprague-Dawley (SD) rats induced by DMBA. METHODS: The 50 SD rats were divided into five groups. Group I (normal control) was given standard drinking and food. Group II was given thymoquinone, Group III was given tamoxifen, Group IV was given DMBA, and Group V was given solvent control. Thymoquinone, tamoxifen, and solvent control administration started 2 weeks before DMBA administration and continued during DMBA induction. In the 3rd week, except for the normal group, all groups were created to be induced with 10 × 20 mg/kg body weight of DMBA for 5 weeks. In the 21st week, surgery and data collection were performed. The hematology profile and CD4CD25Treg number were carried out employing a flow cytometer. The difference in the average number of CD4CD25Treg and blood cells between groups was analyzed with one-way analysis of variance RESULTS: The results revealed that DMBA induction reduced the number of erythrocytes, HB levels, platelet counts, and leukocyte counts (p < 0.05). The administration of thymoquinone and tamoxifen reduced the hematopoiesis effect of DMBA. The thymoquinone and tamoxifen group had a higher number of CD4CD25Treg and leukocytes than the DMBA group (p < 0.05). CONCLUSION: There was no difference in the average CD4CD25Treg, leukocyte count, lymphocyte count, and monocyte count between the thymoquinone and the tamoxifen groups (p > 0.05).