An automated experimental apparatus was used to measure the equilibrium liquid and vapor phase compositions and densities, and interfacial tensions for ethane + 1-methylnaphthalene at 344.3 K. The phase composition data can be described within 0.0005 in mole fraction, the phase densities within 3 kg/m(3), and the interfacial tensions within 5%, using scaling-law-based smoothing functions. The present measurements constitute a useful complement to existing literature data.