Abstract： We studied surface enhanced Raman scattering (SERS) from Benzoic Acid (BA), Salicylic Acid (SA) and P-Hydroxybenzoic Acid (PHBA) in silver sols. The enhanced Raman spectra are recorded and analyzed. The three molecules all contain vibration of ν(C-CO2-) and two of them (SA and PHBA) contain vibration of ν(C-OH), but located at different position. Making use of this situation, we analyzed the dependance of enhancement factor on the distance and orientation of the vibration dipoles relative to the surface and also compared with the pure electromagnetic model for SERS. An apparent discrepancy were revealed. The possible origins are disscussed. We also discussed the influence of coagulation of silver particles on the enhancement factors and pointed out the way for optimizing the enhancement in silver colloid.