Abstract: Process for the manufacture of t-butanol by hydration of isobutylene by reaction of isobutylene or isobutylene-containing C.sub.4 -hydrocarbon mixtures at moderately elevated temperature with aqueous sulfuric acid and isolation of the t-butanol from the resulting solution of t-butanol in water and sulfuric acid, wherein the reaction is carried out at temperatures of from 20.degree. to 45.degree.C using 20-48% w/w aqueous sulfuric acid, the t-butanol being separated from the t-butanol solution in water and sulfuric acid by extraction, at temperatures of from 0.degree. to 50.degree.C, with saturated or mono-olefinically or di-olefinically unsaturated aliphatic or cycloaliphatic hydrocarbons containing at least 3 carbon atoms or with aromatic hydrocarbons of from 6 to 10 carbon atoms or with a mixture of said hydrocarbons, whereupon the t-butanol is isolated from the extracted mixture of t-butanol and hydrocarbon or hydrocarbon mixture.