Eleven ionic liqs. were used as medium of the Die Is-Alder reaction between cyclopentadiene and dimethyl maleate carried out at 25 degrees C to det. reaction rate constants and stereoselectivities correlated with Kamlet-Taft polarity parameters and viscosity of the ionic liqs. Multidimensional linear regression model was chosen. The H bond donating ability and viscosity of ionic liqs. had a significant impact on the reaction rate const. Polarizability contributed to a large extent to the changes in stereoselectivity, whereas H bond-accepting and donating abilities were of lesser importance.