We investigated the effects of grain boundary diffusion (GBD) at elevated temperatures on Auger electron spectroscopy sputter depth profiles of Co-Ag bilayers by using the modified surface accumulation method which is proposed for the first time to our knowledge. The results agree well with our previous ones done by the surface accumulation method. The GBD parameters for Ag in Co along the grain boundaries were found to be as follows : the activation energy and pre-exponential factor for GBD are 0.425 +/- 0.025 eV and similar to 1 x 10(-7) cm(-2), respectively. These indicate that the modified method is an effective alternative in studying the effects of GBD, and may be applied to complicated systems for which the previous method does not hold.