The contact angle, contact angle hysteresis, and interfacial tension were measured using a model system consisting of mercury and halide aqueous solutions. The measured contact angle hysteresis was discussed in terms of the surface roughness, chemical heterogeneity, and mechanical instability. The experimental results of contact angle measurements were analyzed using the surface force theory of wetting films, which demonstrated the presence of hydrophobic forces. The origin of the hydrophobic force observed in the present system was discussed briefly. The importance of hydrated halide anions in controlling the wettability of mercury surfaces was demonstrated. Finally, a correlation between the interfacial tension and hydrophobic force was illustrated.