Objective: This study explored the association between serum nicotinamide phosphoribosyltransferase (NAMPT) and hepatic de novo lipogenesis (DNL) in nonalcoholic fatty liver disease (NAFLD) and determined whether or not this association is sex dependent.Subjects And Methods: In this cross-sectional study, 62 consecutive patients (32 males, 30 females) with NAFLD were recruited. Serum NAMPT (by ELISA), palmitic acid, and the DNL index of erythrocyte membranes as markers of hepatic DNL (by gas chromatography) were analyzed. The controlled attenuation parameter (CAP) and body impedance analyzer were used to assess hepatic and body fat, respectively. Univariate and multiple linear regressions (to adjust for confounders) were used to analyze the association of serum NAMPT with palmitic acid, DNL index, CAP, and body fat.Results: The respective values of serum NAMPT (2.44 ± 1.03 vs. 2.45 ± 1.13 ng/mL, p = 0.98), DNL index (3.11 [2.60-3.71] vs. 3.05 [2.40-3.59], p = 0.90), and palmitic acid (20.55% [15.34-24.04] vs. 22.64% [21.15-25.95], p = 0.07) were not significantly different between men and women, but those of CAP (326 [300-340] vs. 300 [261.25-329], p = 0.002) and body fat (37.71 ± 3.80 vs. 26.60 ± 5.70, p < 0.001) were significantly higher in women. In women, serum NAMPT had a significant negative association with the DNL index (β = -0.56, p = 0.01). The DNL index also had a significant negative association with body fat (β = -0.46, p = 0.02). In men, the only significant association was the positive association between serum NAMPT and CAP (β = 0.35, p = 0.035).Conclusion: Higher serum NAMPT in women was associated with a lower hepatic DNL index, while in men it was associated with higher hepatic fat and had no association with the DNL index. Therefore, the serum NAMPT level interpretation for NAFLD prognosis is probably sex dependent.