The structure of sulfoalkylated cyclodextrins (CDs) have been varied and optimised to improve their performances as mass-transfer promoters in an aqueous biphasic hydroformylation reaction. Their surface tensions have been measured using the Wilhelmy plate technique and compared. Their behaviour towards two hydrosoluble derivatives of triphenylphosphine has been evaluated by P-31{H-1} and H-1 NMR measurements and their catalytic activity has been assessed in a rhodium-catalyzed hydroformylation reaction of 1-decene. The best result was obtained using a beta-CD sulfobutylated on the primary face and methylated on the secondary face. Indeed, this CID increased the reaction rate by a factor of 250 without inducing selectivity decrease. The accessibility to the secondary face of the CID appears to be determining in the catalytic process as it governs the approach between the CD-included substrate and the water-soluble catalyst. The impact of the nature of the CID substituents on the chemo- and regioselectivity of the reaction is also discussed. (C) 2008 Elsevier B.V. All rights reserved.