Densities and viscosities of salicyl amide, salicylic acid, and acetyl salicylic acid (non-steroidal anti-inflammatory drugs) in two aprotic solvents namely, dimethyl sulfoxide and acetonitrile at T = (293.15, 298.15, 303.15, 308.15, 310.15, and 313.15)K have been determined in a molality range of (9.7. 10(-3) to 33.3 . 10(-3)) mol . kg(-1). The data have been used to calculate apparent molar volumes (V-phi), and viscosity B-coefficients. The partial molar volumes and hydration numbers have been determined at different temperatures. The effect of temperature on the thermodynamic properties has been studied by determining partial molar expansibilities (partial derivative V-m(0)/partial derivative T) anti Hepler's constant (partial derivative V-2(m)0/partial derivative T-2). Free energies of activation for viscous flow of the solution were obtained by application of the transition state theory of solutions to the B-coefficient data and the corresponding activation enthalpies are reported. (C) 2010 Elsevier Ltd. All rights reserved.