Abstract The BCC Fe –Al system has been modeled with the Monte Carlo (MC) method in the grand-canonical ensemble calculation using the Ising model. The present calculation was performed in isothermal conditions with a computer crystal with 483 atoms at 1000 K. The interaction parameters for this calculation were taken from a previous Cluster Variation Method (CVM), which included tetrahedron interactions. The comparison of the integral thermodynamic properties (internal energy and equilibrium alloy composition) obtained in both calculations shows good agreement. Small deviations are observed only in the neighborhood of the second-order B2/A2 critical composition.