Abstract: A process for purifying isoprene produced by catalytic decomposition of dimethyldioxane from carbonyl compounds and cyclopentadiene which involves passing isoprene at a temperature of 40.degree. to 70.degree. C. through a bed of a solid product such as an anion exchange resin or alkali (the latter may be used with or without an inert carrier), followed by subjecting the isoprene to close fractionation performed with at least 50 theoretical plates and at a reflux ratio of at least 3. The process of the present invention enables practically complete purification of isoprene from carbonyl compounds and cyclopentadiene. The purified isoprene, when used as a monomer in the production of stereospecific isoprene rubber, results in high-quality products; and reduces by a factor of 2-3 the Ziegler catalyst consumption in the isoprene rubber synthesis.