In this paper, we have derived an equation of state (EoS) for liquid alkali metals based on a suggested potential function over the whole liquid range including metal-nonmetal transition. This EoS is based on the interaction of nearest neighbors according to the characteristics of the soft repulsive interaction in dense and large attractive interaction in expanded liquid alkali metals. PVT data of dense liquid alkali metals obey the equation (2Z - 1)V-m = A + B rho over the whole range of liquid densities, where Z, V-m, and rho are compression factor, molar volume, and molar density, respectively. The intercept A and slope 8 of this equation are related to the attractive and repulsive parts of suggested potential function, respectively, and both depend on temperature. The new EoS has been used to calculate the molar density and other thermodynamic properties such as isobaric expansion coefficient, alpha(p): isothermal compressibility, K-T; and internal pressure, P-i: of liquid alkali metals at any temperature and pressure over the whole liquid range. The results show good agreement between the values obtained using this equation and the experimental and literature data. To show the ability of this EoS in prediction of thermodynamic properties of liquid alkali metals over the whole liquid range, the results have been compared with some other equations. (C) 2012 Elsevier B.V. All rights reserved.