1-Butane and isobutene are effectively separated without isomerization of 1-butene by contacting an isobutene-containing hydrocarbon mixture with a solid acid catalyst having a solid acid quantity of 0.05 to 0.25 mmol/g of solid acid catalyst, represented by the adsorption quantity of pyridine, thus low-polymerizing selectively isobutene and then separating the low polymers of isobutene from 1-butene.