A novel one-handed helical poly(phenylacetylene) bearing L-hydroxyproline pendants (poly(PA-P)) was synthesized as an eco-friendly polymer-supported catalyst for asymmetric reactions. The helical poly(PA-P) catalyzed the asymmetric aldol reactions of cyclohexanone with p-nitrobenzaldehyde, and showed good recyclability and higher enantiomeric excess (ee) in aqueous medias than that in organic medias. The one-handed helicity of poly(PA-P) was clearly affected by the water content in the aqueous media. The helical poly(PA-P) showed the higher enantioselectivity (ee = 99%) than its monomer PA-P (ee = 54%) in THF/H2O (H2O vol % = 25.0 vol %). After the one-handed helical structure of poly(PA-P) was destroyed by grinding treatment, the ee of the reaction clearly decreased from 99 to 49%. These indicate that the one-handed helical structure of poly(PA-P) played an important role in the high enantioselectivity of the asymmetric aldol reactions in the aqueous media. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1024-1031