A solution treated coarse grained (CG) Al6061 was subjected to high pressure torsion (HPT) at room temperature resulting in the formation of a homogeneous ultra-fine grained (UFG) microstructure with an average grain size of 170 nm. Tensile tests were performed at room temperature (RT) and liquid nitrogen temperature (LNT). The as-HPT UFG Al6061 alloy shows an increased strength at both RT and LNT. The decrease of testing temperature results in increased flow stress and in enhanced elongation to failure in both CG and UFG samples. The ratio σ_y ^LNT/σ_y ^RT was found to be larger for the CG Al6061 than for the UFG Al6061. Both surface relief and fracture surface observations were performed. The effect of the grain size and of the testing temperature on the mechanical behaviour of the Al6061 alloy is analyzed in detail. It is suggested that the solute atoms play an important role in the plastic deformation of the UFG Al6061 alloy.