We propose to carry out isotopic analysis of three light elements, namely boron, carbon, and nitrogen, in pristine silicate grains of Itokawa returned by the Hayabusa-I spacecraft using secondary ion mass spectrometry (SIMS). Those grains were in the asteroid regolith, and are known to have been exposed to the solar wind based on the noble gas measurements. Therefore, one would expect that other elements in the solar wind would also be implanted into the shallow layers of these particle samples. The main scientific goal of this proposal is to determine the solar-wind-implanted B, C, and N isotopic compositions in the unpolished Itokawa samples and to derive the isotopic ratios of these elements of the Sun from the solar wind values. Although the N isotopic composition of the solar wind has been revealed by the measurements of Genesis-mission samples, those of the other two elements are still unknown. The results from the proposed effort will be able to provide information on those missing pieces.