Vapour pressures of n-butanol with 2-methylpentane and 3-methylpentane between 283.15 and 313.15 K were measured at 5 K intervals by a static method. Excess enthalpies and excess volumes, at 298.15 K, were also measured. Experimental excess volumes are compared with predictions of an extended real associated solution (ERAS) model. The model reproduces qualitatively the experimental curves of V(E) and gives a good description of the experimental results of G(E) at 298.15 K.