A sample with nominal composition YFe10.5TiB0.5 has been prepared through careful processing. X-ray diffraction analysis revealed that the main phase in the sample is in the tetragonal ThMn12-type structure (space group, I4/mmm),-and a small amount (less than 3%) of alpha-Fe exists as a second phase. Neutron diffraction measurements indicated that, in the tetragonal structure, the boron atoms occupy the 8i sites, substituting for a few Ti atoms, while the substituted Ti atoms enter the interstitial 2b sites. The real composition of the main phase was determined to be Y(Fe11.04Ti0.52B0.43)Ti-0.39.