Ultrasonic velocity, density, viscosity and surface tension of ionic liquids 1-buty1-3-methyl imadazolium hexafluorophosphate [BMIM][PF6], 1-butyl-3-methyl imadazolium octyl sulfate [BMIM][OcSO(4)] and 1-ethyl-3-methyl imadazolium methane sulfonate [EMIM][MeSO3] have been measured from 303 K to 333 K. Using these experimental data, inter relationships among ultrasonic velocity, density, viscosity and surface tension have been examined for these ionic liquids. It has been found that (a) ultrasonic velocity (u), surface tension (sigma) and density (rho) can be correlated linearly using equation, log u = psi log sigma/rho + xi (with typical values of psi = 1.61 and xi = 10.459) (b) surface tension is linearly correlated with viscosity by the relation In sigma = In a + b eta(-0.125), where In a and b are constants. These correlations among physicochemical properties of the ionic liquids can be used to evaluate the properties (viz, ultrasonic velocity) not available in literature. (C) 2011 Elsevier B.V. All rights reserved.