The　typically-used　element　torsional　stiffness　GJ/L　(where　G　is　the　shear　modulus,　J　the　St.　Venant　torsion　constant,　and　L　the　element　length)　may　severely　underestimate　the　torsional　stiffness　of　thin-walled　nanostructural　members,　due　to　neglecting　element　warping　deformations.　In　order　to　investigate　the　exact　element　torsional　stiffness　considering　warping　deformations,　this　paper　presents　a　matrix　stiffness　method　for　the　torsion　and　warping　analysis　of　beam-columns.　The　equilibrium　analysis　of　an　axial-loaded　torsion　member　is　conducted,　and　the　torsion-warping　problem　is　solved　based　on　a　general　solution　of　the　established　governing　differential　equation　for　the　angle　of　twist.　A　dimensionless　factor　is　defined　to　consider　the　effect　of　axial　force　and　St.　Venant　torsion.　The　exact　element　stiffness　matrix　governing　the　relationship　between　the　element-end　torsion/warping　deformations　(angle　and　rate　of　twist)　and　the　corresponding　stress　resultants　(torque　and　bimoment)　is　derived　based　on　a　matrix　formulation.　Based　on　the　matrix　stiffness　method,　the　exact　element　torsional　stiffness　considering　the　interaction　of　torsion　and　warping　is　derived　for　three　typical　element-end　warping　conditions.　Then,　the　exact　element　second-order　stiffness　matrix　of　three-dimensional　beam-columns　is　further　assembled.　Some　classical　torsion-warping　problems　are　analyzed　to　demonstrate　the　established　matrix　stiffness　method.