Hydration of 5-isoxazolyl-phenyl (or -butyl) acetylenes (1a, b) in dilute sulfuric acid in the presence of mercuric sulfate afforded 5-isoxazolylmethyl phenyl (or butyl) ketones (3a, b), predominantly. In contrast, the hydration of 4-isoxazolyl-phenyl (or -butyl)-acetylenes (2a-d) under identical conditions gave 4-isoxazolyl benzyl (or pentyl) ketones (5a-d) as the main products. The structure of one of these products, 3, 5-dimethyl-4-isoxazolyl benzyl ketone (5a), was determined by Beckmann rearrangement. Isoxazoles containing a cis-alkene or alkane chain were obtained by the catalytic reduction of the above acetylenes without cleaving the isoxazole nucleus.