The electrical conductivity of a number of ionic liquids, 1-propyl-3-methylimidazolium bromide ([PrMIm]Br), 1-hexyl-3-methylimidazolium bromide ([HMIm]Br), 1-octyl-3-methylimidazolium bromide ([OMIm]Br) and 1-decyl-3-methylimidazolium bromide ([DMIm]Br), in the aqueous d-xylose solutions at several concentrations, (0.2, 0.5 and 0.8) mol kg(-1) have been measured at 298.15K. The obtained data have been analyzed using low concentration Chemical Model (1cCM) of conductance equation in terms of ion association constant (K-a), limiting molar conductivity (Lambda(0)), Walden product (Lambda(0)eta) and distance parameter (R). It was observed that the K-a values decrease with increase in both alkyl chain of ionic liquid and D-xylose concentration. Gibbs free energy of ion pair formation (Delta G(a)(0)) was estimated using the K-a values. It was found that the Delta G(a)(0) values are negative and became more negative with shorter alkyl chain length of ionic liquids and low concentration of D-xylose. (C) 2012 Elsevier Ltd. All rights reserved.