We report here the sequential refreshment of a water-immiscible ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P14TFSI) enhanced the production amount of paclitaxel and the related taxanes with in situ extraction from an aqueous medium in a plant cell culture. The production amount of the taxanes with refreshment of 2.5 vol% P14TFSI twice every 2 days was three times greater than that without the refreshment and 600 times greater than that of control culture without P14TFSI. The enhanced production amounts of taxanes in the culture with P14TFSI might be due to the deceased feedback inhibition of paclitaxel and abiotic stress responding against elevation of intracellular production of reactive oxygen species (ROS) derived from P14TFSI's abiotic stress.