PURPOSE: To obtain a butylene polymer free of unpleasant odors in good efficiency, by deodorizing the polymer after polymerization by using a silica-alumina adsorbent.

CONSTITUTION: In producing a butylene polymer by polymerizing butylene, the polymer is deodorized by using a silica-alumina adsorbent containing 5W20wt% silica. This adsorbent is produced by a method comprising kneading silica gel with alumina gel in a wet state, a method comprising simultaneous gelation of silica and alumina from an aqueous solution, a method comprising combining silica gel with an aluminum salt by an immersion method, or a like method. In addition, this adsorbent is regeneratable and can be regenerated at a % recirculation of 90% or higher. The butylene polymer thus produced is substantially free of unpleasant odors and excellent as a solvent. Therefore, it is particularly suitable as a solvent for insecticides.