Coexistences curves of liquid-liquid phase transition were reported for the binary solutions of the room temperature ionic liquid (RTIL) 1-octyl-3-methylimidazolium hexafluorophosphate ([C(8)mim][PF6]) with 1-propanol or tert-butanol. The critical amplitude B and the critical exponent beta corresponding to the coexistence curve were deduced and the values of beta were found to be consistent with the 3D-Ising value. Asymmetry of the diameters for the coexistence curves were examined and discussed in the frame of the complete scaling theory. (C) 2014 Elsevier B.V. All rights reserved.