Vitamin A acid (VAA) was firstly dissolved in chloroform, and then the organic solution containing the samples was mixed with silver sol at the desired concentration. After sufficient shaking, collect SERS spectra of VAA with silver sol layer solution. The attribution of the peaks was illustrated by comparing SERS spectra with NR (Normal Raman) spectra, and the mechanism and orientation of adsorption were also discussed according to the peaks which was absent in NR spectrum but observed in SERS spectrum. To verify the feasibility of the method for the quantitative analysis, SER spectra at different concentration of VAA were collected. The intensities measured with the band at 1583 cm(-1) were plotted as a function of concentration. It was found that an effective limit for the detection of VAA could be as low as to 1.0 x 10(-7) mol x L(-1), the calibration curve was linear in the range from 1.0 x 10(-6)-5 x 10(-5) mol x L(-1). The proposed method has the potential to quantitative assay of the drugs having SERS effects but undissolvable in water.