This paper presents a flexural–torsional analysis of composite box beams. A general analytical model applicable to thin-walled box section composite beams subjected to vertical and torsional load is developed. This model is based on the classical lamination theory, and accounts for the coupling of flexural and torsional responses for arbitrary laminate stacking sequence configurations, i.e. unsymmetric as well as symmetric. Governing equations are derived from the principle of the stationary value of total potential energy. Numerical results are obtained for thin-walled composites beams under vertical and torsional loading, addressing the effects of fiber angle and laminate stacking sequence.