The melting temperature of the l-methylnaphthalene-indole system has been measured with a direct visual observation method at temperatures from 277 to 334 K and pressures up to 284 MPa. The high pressure solid-liquid equilibria(SLE) for the 1-methylnaphthalene-indole system have been determined from the melting temperature data. The PVTx relationships of the same system has been measured at temperatures from 293.15 to 363.15 K at 0.1 MPa and pressures up to 300 MPa at 333.15 K. The Carnahan-Starling-van der Waals(CS-vdW) equation of state was used to correlate the PVTx data. The high pressure SLE were predicted with the CS-vdW equation of state for the liquid phase and the Birch equation for the solid phase. In order to test the effect of the mixing rule for the liquid phase on the prediction results, two models were applied : that is the van der Waals one-fluid model and the excess g(E) free energy model of Heidemann and Kokal(1990). It was found that the one-fluid model gives better results than the g(E) model, especially near the eutectic.