Tensile test on smooth and circumferentially notched specimens, systematic observation of fracture surfaces and large deformation finite element analysis were conducted to understand the deformation and failure behavior of a magnesium alloy (AM60). The plastic deformation is considered to be dominated by twining mediated slip. The tensile properties were not sensitive to the strain rates applied (3.3 x 10(-4) similar to 0.1). Corresponding to the same loading level, higher stress triaxiality but lower plastic strain was observed in the specimens with a smaller notch profile radius. Deformation and failure of the magnesium alloy were sensitive to the constraint level and ductile-brittle fracture transition occurred with decreasing the notch profile radius.