Objective:To study the inhibition of fatty acid synthase (FAS) by Xuezhiling tablets in vitro

and explore its mechanism of action. Method: The ultraviolet spectroscopy was used to evaluate the activity of FAS through monitoring the alteration of absorbance(A) value of reduced nicotinamide-adenine dinucleotide phosphate(NADPH) and the substrates were respectively acetyl coenzyme A(AcCoA)

malonyl-CoA(MalCoA)

acetoacetyl-coenzymeA(AcAcCoA)

ethyl acetoacetate

ethyl crotonate

NADPH for different active sites. The inhibition of FAS by overall reduction and different active sites was separately detected after the treatment with different doses of Xuezhiling tablets. Result: The activity of FAS could be inhibited by Xuezhiling tablets. After the treatment with Xuezhiling tablets (150 mg·L-1)

the inhibition ratio was 51% with manner if time and dose relationship. For the different active sites of FAS

Xuezhiling tablets displayed different abilities. It showed more potential in inhibiting the enoyl reduction and AcAcCoA reduction than keto-acyl reduction

and it was also dose dependent for the different active sites. The residual activity of different active sites was less than 70%

and more than 50%

when FAS was treated with Xuezhiling tablets at the concentration of 150 mg·L-1. Conclusion: FAS can be inhibited by Xuezhiling tablets

and this ability was attributed to inhibit the different active sites of FAS. This article prove that the ratiocination about the lowering blood lipids of Xuezhiling tablets is related to FAS and it can be a reference for Xuezhiling tablets used for obesity and other disease that related to FAS.