L-Proline moieties, which serve as organocatalysts, were tethered on block copolymers that consisted of thermoresponsive poly(N-isopropylacrylamide) and PEG-grafted polyacrylate blocks. The copolymer dissolved in water at temperatures below the LCST (25 degrees C), whereas they formed micelles at temperatures above the LCST (50 degrees C). Aldol reactions between an arylaldehyde and a ketone were conducted in this aqueous solution. The aldol products were obtained in high yield with high diastereo- and enantioselectivity (96% ee). The catalyst solution could be reused up to three times.