We have investigated adsorption of molecules with hydroxyl group, ROH, on sodium halide cluster ions, NanXn-1+ (X = F and 1, n = 10-17) by mass spectrometry and by theoretical calculations. From analysis of the cluster ion intensities, the adsorption of one water molecule (R = H) is most efficient for Na13X12+, whose structure has a NaX defect from it 3 x 3 x 3 Cubic structure of n = 14. This result Suggests that the defect has an important role in the adsorption reaction. However, it. is also found that the reactivity diminishes with increasing bulk size of the R group from H to CH3, (CH3)(2)CH, and (CH3)(3)C. These results imply that the adsorption reactivity is dominated by steric hindrance; the smaller molecules are adsorbed inside the basket Structures of Na13X12+. Reactivity dependence on the basket size is also discussed by comparing the results of NanFn-1+ and NanIn-1+.