Skeletal isomerization of n-alkenes into isoalkenes and enrichment of isoalkenes in alkene-containing hydrocarbon mixtures is effected in the presence of an isomerization catalyst containing a microporous silicon-containing alumophosphate.A goal of the method for skeletal isomerization is to provide a running time in one operating period of over 100 hours. This goal is achieved by using, as isomerization catalysts, microporous alumophosphates with a molecular sieve structure whose pore inlet openings have a diameter of 0.4 to 0.6 nm which are mixed with a binder and activated at temperatures of 623 to 873K.