We propose to perform oxygen three-isotope analyses of Itokawa silicate grains using a new generation multi-collector Secondary Ion Mass Spectrometer at the University of Wisconsin (WiscSIMS). We aim to reassess oxygen isotope analyses made by HAPSET, which show a large variation in 18O/16O ratios that is significantly more than that obtained from LL chondrites. We will use a primary beam size that is approximately 10 μm in order to achieve sub permil precision in oxygen three-isotope ratios. We will use a new sample mounting procedure in order to eliminate possible SIMS instrumental mass fractionation produced by surface topography of samples. We request 14 grains from those in polished mounts and unprocessed grains. We will examine surface topography of polished grains using a ZYGO white light profilometer, because extensive electron microscopy during Initial Analysis Activity may have damaged epoxy resin around the target grains. Additional electron microscopy will be minimized prior to SIMS analysis in order to avoid additional beam damage. The SIMS analyses leave pits of 10-15 μm diameter and 1 μm deep on sample surface. Minimal consumption of sample is expected from the processes of removing previous SIMS pits made by HAPSET and polishing of newly mounted grains. New oxygen isotope data from WiscSIMS will constrain thermal evolution of the parent asteroid of Itokawa grains.