The excess enthalpies and excess volumes of 1-aminobutane, 1-amino-2-methylpropane, 2-aminobutane and 2-amino-2-methylpropane with acetonitrile were determined at 303.15 and 298.15 K, respectively, using a microcalorimeter and a densimeter. Dissociation of self-associated amine species and formation of amine-acetonitrile complexes were expected to take place in solution. The excess enthalpies were positive and the excess volumes were negative for all four systems. The enthalpies of complex formation were calculated from the partial molar enthalpies. The endothermic heats of mixing and negative volume change on mixing are explained in terms of the extent of formation of amine-acetonitrile complexes in the liquid mixtures.