PURPOSE: To obtain a purified isoprene derivative in high yield, by dissolving crude isoprene derivative in a mixture of water and an organic solvent, adsorbing the isoprene derivative with a hydrophobic adsorbent, and desorbing with an organic solvent free from water.

CONSTITUTION: Crude isoprene derivative such as vitamin K, coenzyme Q, etc. is dissolved in a mixture of water and an organic solvent, and the solution is made to contact with a hydrophobic adsorbent at room temperature W normal temperature to effect the adsorption of the isoprene derivative. Purified isoprene derivative is prepared by desorbing the adsorbed derivative with an organic solvent essentially free from water at room temperature W normal temperature. The hydrophobic adsorbent is preferably chemically bonded silica gel containing smallest possible amount of residual silanol group, preferably the product obtained by the reaction of organic silane with silica gel, or a porous synthetic resin such as commercially available Amberlite, Hiporous, etc.

EFFECT: A large amount of crude isoprene can be purified for a long period with simple operation.