Stress–strain characteristics of Al–0.86wt%Mn–0.28wt%Fe specimens with different grain diameters were studied in the temperature range from 300 to 393K. Tensile tests were performed at different strain rates ranged from ε˙=2.2×10 −4 to 1.0×10 −2 s −1 . The work hardening parameters; yield stress σ y , fracture stress σ f , strain hardening exponent n, and the total elongation ɛ T were found to be markedly affected by the strain rate ε˙, deformation temperature T and grain diameter D of the tested sample. From the grain diameter dependence of these hardening parameters, two distinct stages were observed. In the first stage, increasing D results in increased σ y , σ f , n and ɛ T to maxima at ∼53μm. In the second stage, these parameters drastically decreased with further increase of D. The decrease of σ y with D in the second stage reaches its minimum (σ y,min ) at values depend on the strain rate ε˙. Both σ y and σ y,min were found to increase with increasing ε˙ while ɛ T decreased. The obtained results were interpreted on the basis of solid solution decomposition caused by annealing treatment. The grain diameter dependence of the work hardening parameters may characterize a dislocation movement by cross slip mechanism. The microstructure of the tested samples was examined by optical microscopy and X-ray diffraction measurements.