Unequal-leg　angles　can　be　used　to　provide　more　efficient　design　in　specific　cases,　but　the　behaviour　of　unequal-leg　angles　has　received　much　less　attention　than　equal-leg　angles.　This　paper　studies　the　flexural　and　torsional　buckling　modal　participation　and　investigates　the　structural　behaviour　of　aluminium　alloy　unequal-leg　angle　columns.　The　experimental　programme,　which　was　carried　out　on　two　unequal-leg　angle　cross-sections,　included　material　coupon　tests,　initial　geometric　imperfection　measurements　and　a　total　of　eight　column　tests.　The　test　setup,　procedure　and　results　are　fully　reported.　Following　the　experimental　investigation,　numerical　models　were　developed　and　validated　against　the　test　results.　Upon　validation,　a　series　of　parametric　studies　were　carried　out　to　analyse　the　influence　of　width-to-thickness　ratio　and　aspect　ratio　on　the　flexural　and　torsional　buckling　modal　participation.　The　ultimate　resistances　obtained　from　simulations　were　used　to　assess　the　accuracy　of　the　current　design　provisions　given　in　the　European　standard　for　aluminium　alloy　structures.　The　result　comparison　shows　that　the　existing　design　provisions　yield　inaccurate　predictions　for　unequal-leg　angle　columns.　Considering　mode　interaction,　a　more　accurate　and　convenient　design　method　was　proposed　for　unequal-leg　angle　columns.