Hybrid of graphene or graphene oxide (GO) with gold or silver nanoparticles (AgNPs) as substrate for SERS detection often brings large background and low signal to noise ratio, which leads to poor sensitivity. In this study, it is proposed that the silver loading amount on GO and dosage of GO-Ag composite have significant influence on its SERS activity (SERS signal intensity and signal to noise ratio). The adsorption ability and SERS activity of GO-Ag composite for several dye molecules were investigated in detail. It was found increasing the dosage of GO-Ag or AgNPs loading on GO always enhances its absorption to dye molecules, while in both cases the SERS signal first increase and then decrease. The reason for this fluctuation of SERS signal was investigated and discussed, which indicate high silver loading amount leads to enhanced background response, while high composite dosage could decrease the signal of target molecule. Finally, an optimized GO-Ag substrate providing strong SERS signal and high signal to noise ratio was used for the detection of several dye molecules by SERS with the lowest detectable concentration down to 1 mu M. Our results indicated that great caution should be paid on the silver loading amount and dosage of GO-Au/Ag when using GO-Au/Ag as SERS substrate for molecule sensing or comparing different results reported in reference. (C) 2015 Elsevier B.V. All rights reserved.