Microwave-assisted ring-opening polymerization of epsilon-caprolactone in the presence of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid using zinc oxide as a catalyst is investigated. By adding 30 wt.-% ionic liquid, poly(epsilon-caprolactone) with a weight-average molar mass os 28 500 g . mol(-1) is obtained at 85 W for 30 min. The results indicate that the polymerization could be efficiently enhanced in the presence of ionic liquids under microwave irradiation because ionic liquids can effectively absorb microwave energy.