Electrodeposited　copper　samples　composed　of　columnar　grains　subdivided　by　alternating　twin/matrix　(T/M)　lamellae　have　been　cold　rolled　to　30-85%　reduction　in　thickness.　The　thickness　of　the　T/M　lamellae　varies　over　a　wide　range　from　a　few　nanometres　to　about　1　m.　The　deformation　microstructure　has　been　characterized　systematically.　In　thin　T/M　lamellae　(below　50-100　nm)　the　deformation　behaviours　differ　significantly　from　that　of　thick　T/M　lamellae,　as　the　dislocation　activity　is　concentrated　at　the　T/M　boundaries　illustrated　by　the　observations　of　stacking　faults　and　Shockley　partial　dislocations.　In　thick　T/M　lamellae　(100-1000　nm),　the　deformation　microstructure　is　related　to　the　grain　orientation　as　also　observed　previously　in　deformed　single　crystals　and　polycrystals　with　a　grain　size　at　the　micrometre　scale.　The　experiment　therefore　suggests　that　the　universal　structural　characteristics　of　deformation　microstructure　can　be　extended　one　order　of　magnitude　from　about　5　m　to　the　sub-micrometre　scale　(about　0.5　mu　m).