A new surface tension equation based on the thermodynamic definition of surface tension and the expression of Gibbs free energy is proposed, which is different from existing ones with respect to theoretical background and formulation. By using the Wilson equation to represent the excess Gibbs free energy, a two-parameter surface tension equation is derived for liquid mixtures. The feasibility of the equation has been tested in terms of correlation for 124 binary systems and by prediction for 16 multicomponent systems at ambient temperatures with overall average absolute relative deviation (AAD) of 0.54 and 1.36%, respectively. The model parameters obtained by correlating binary surface tension at one temperature can be used to predict surface tension at other temperatures with good accuracy. It is shown that the new equation is simple in terms of calculation, accurate in correlation and prediction and is applicable to large variety of systems.