OBJECTIVE To investigate the effect and mechanism of high dose Vitamin B3 on granulopoiesis in normal rat. METHODS Twenty one healthy SD rats were randomly divided into three groups: the Vitamin B3 group (Vit B3 500 mg·kg⁻¹·d⁻¹, × 7 d), the rhG-CSF group (rhG-CSF 25 μg·kg⁻¹·d⁻¹, × 7 d) and the normal saline group (2 ml/d, × 7 d). The peripheral blood cell counts were analyzed by automatic blood cell counter before (day 0) treatment, the third day (day 3) and the seventh day (day 7) after administration of drugs, respectively. The concentration of serum nicotinamide adenine dinucleotide (NAD⁺) level was measured by enzymatic cycling assay before and after drugs treatment. The expressions of G-CSF, G-CSFR, SIRT1, C/EBPα, C/EBPβ, C/EBPε and NAMPT mRNA were detected by reverse transcription real-time fluorescent quantitative PCR. RESULTS The neutrophil counts increased significantly after 7 days of Vitamin B3 and rhG-CSF treatment compared with that of control group [(1.64 ± 0.19) × 10⁹/L, (1.88 ± 0.37)× 10⁹/L vs (0.86 ± 0.18) × 10⁹/L, P<0.01]; the level of serum NAD⁺ increased significantly [(0.96 ± 0.08) nmol/L, (0.65 ± 0.12) nmol/L vs (0.36 ± 0.15) nmol/L, P<0.01]; the expression of G-CSF, G-CSFR, SIRT1, C/EBPα, C/EBPε and NAMPT mRNA in bone marrow mononuclear cells were increased significantly compared with that of control group (P<0.01). CONCLUSION High dose of Vitamin B3 may play an important role in increasing absolute neutrophil count in healthy rat under steady state, and the mechanism may be dependent on NAMPT-NAD⁺-SIRT1 signaling pathways.