High precision Sr isotope ratios (^87Sr/^86Sr) have been determined for GSJ reference samples JB-1a, JB-2, JB-3. JA-3 and JG-1a, using a MAT262 mass spectrometer in the Department of Geology, Shimane University. During the course of this study, Sr isotope ratios of NBS987 were measured twice, giving values of 0.710276±0.000007 (2σ)and 0.710274±0.000007 (2σ).