A highly selective and active catalyst for the positional isomerisation of 2-butene into 1-butene has been developed by using a mesoporous silica, MCM-41. The yields of 1-butene as well as total conversion decrease when aluminium or lanthanum was added to the MCM-41 even though the amounts of acid sites increase. FT-IR spectra proved that the H site due to the silanol group may act as an active site for the positional isomerisation of 2-butene to 1-butene.