The catalytic isomerisation of dimethyl ethynylcarbinol-1 with the formation of beta-methylcroton-aldehyde-2 was carried out in the presence of oxometallic derivates in a heterogeneous vapour phase process. The MoO3-SiO2 catalysts, prepared by impregnation are particularly efficient : a 75% selectivity could be obtained. The only by-product is methyl-2-butene-1-yne-3. Mechanistic explanations are proposed and catalyst design are given in relation to the liquid phase homogeneous process.