Asteroid 4 Vesta is thought to be a differentiated object with intact internal structure due to its achondritic surface. In this paper, we report K-L band spectroscopic observations of Vesta. We have detected the presence of a 3-¿m absorption feature at about the 1% level on the surface of Vesta at longitudes between 155¿ and 195¿. This result indicates that OH and/or H2O-bearing minerals are present in this region of Vesta; the sources are plausibly fragments of carbonaceous chondrite impactors or solar wind implantation. The detection of 3-¿m absorption features from Vesta, regarded as the smallest terrestrial planet, may provide clues to the origin of volatile materials on terrestrial planets.