In this study, a new ionic liquid co-solvent is proposed and optimized for the extraction of paclitaxel from plant cell culture. When using an ionic liquid ([Bmim]BF4) as co-solvent, most of the paclitaxel (similar to 90%) was recovered from biomass by extracting once for 30 min at a ratio of ionic liquid to methanol of 0.166:1 (w/w) and a ratio of solvent to biomass of 1:1 (v/w) at room temperature. In addition, when the pH of the extracting solution containing an ionic liquid as co-solvent was reduced, the paclitaxel recovery increased. When paclitaxel was extracted from glycoside-containing biomass using an acidic ionic liquid ([Bmim]BF4) as co-solvent (pH: 2.2), paclitaxel recovery was high (1.4-fold increase compared to control) due to glycoside hydrolysis arising from a low pH (acidic conditions) of the extracting solution as well as good extractability of ionic liquid itself. (C) 2015 Elsevier Ltd. All rights reserved.