Background: Safflor yellow A (SY) has been demonstrated to be beneficial to cardiovascular system. Our previous study showed that hydroxysafflor yellow A (HSYA), a main component of SY, could increase peroxisome proliferator-activated receptor gamma mRNA expression. In this study, we investigate the effect of HSYA on the proliferation and adipogenesis of mouse 3T3-L1 preadipocytes. Methods: The proliferation and adipogenesis of 3T3-L1 cells treated with HSYA was studied by 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl tetrazolium bromide (KIT) spectrophotometry, Oil Red O staining and intracellular triglyceride assay methods. HSL mRNA expression and promoter activity were studied by real-time quantitative RT-PCR, transient transfection and dual luciferase reporter gene methods. Results: HSYA (0.1 mg/L) significantly inhibited the proliferation of 3T3-L1 cells when compared with control cells in 8 h. This effect was further enhanced with the extension time (24 to 96 h) and an increase of concentration of HSYA (1-10 mg/L). The maximal inhibitory action was observed at 0.1 mg/L HSYA in 72 h (86 +/- 11.8% vs. 100 +/- 4.1%, p < 0.01). HSYA notably reduced the amount of intracellular lipid and triglyceride content in adipocytes to 85% (1 mg/L) and 75% (100 mg/L) on Day 4 following the differentiation, respectively, while increased HSL mRNA expression and promoter activities to 2.7 fold and 1.55 fold, respectively (p < 0.01), in differentiated 3T3-L1 adipocytes. Conclusions: HSYA inhibits the proliferation and adipogenesis of 3T3-L1 preadipocytes. The inhibitory action of HYSA on adipogenesis may be due to the promotion of lipolytic-specific enzyme HSL expression by increasing HSL promoter activity. (C) 2014 Elsevier B.V. All rights reserved.