The Sr isotopic composition of foraminifera has been used in studies of chronstratigraphy and sedi- mentary geochemistry. However, it is difficult to sample foraminifera without overprinting of later diagenesis, which contains enough amount of Sr for isotopic measurement. Analysis of single-grain foraminifera was successively conducted by a combination of low Sr procedural blank and high precision determination of 87Sr/86Sr ratio. This combi- nation of single-grain foraminifera can be significant for the study and application of Sr isotopic composition of fo- raminifera. Measured foraminifera of this study, having a size between 250 μm and 400 μm, were sampled from the carbonate basement of a ferromanganese crust in western Pacific. Mean value of 87Sr/86Sr ratios of the analyzed sin- gle-grain foraminifera is 0.709150 ±0.000013 with internal precision between 4 ppm and 8 ppm for each measurement run. Average value of total procedural blank of Sr is 14 pg. It is significant but difficult to date foraminifera in carbonate basements of ferromanganese crusts. Based on the ob- tained value of 87Sr/86Sr ratio, the analyzed foraminifera can be dated at 0.91 +0.33/?0.39 Ma. The Sr isotopic composition of foraminifera has been used in studies of chronstratigraphy and sedimentary geochemistry. However, it is difficult to sample foraminifera without overprinting of later diagenesis, which contains enough amount of Sr for isotopic measurement. Analysis of single-grain foraminifera was successively conducted by a combination of low Sr procedural blank and high precision determination of 87Sr / 86Sr ratio. This combi- nation of single-grain foraminifera can be significant for the study and application of Sr isotopic composition of fo- raminifera. Measured foraminifera of this Mean value of 87Sr / 86Sr ratios of the analyzed sin- gle-grain foraminifera is 0.709150 ± 0.000013 with internal precision between 4 ppm and 8 ppm for each measurement run. Average value of total procedural blank of Sr is 14 pg. It is significant but diffi cult to date foraminifera in carbonate basements of ferromanganese crusts. Based on the obstructed value of 87Sr / 86Sr ratio, the analyzed foraminifera can be dated at 0.91 + 0.33 /? 0.39 Ma.