In order to study the effect of laser shock processing (LSP) on mechanical properties of magnesium alloys, the tensile stress-strain curves and microstructures of AZ31 and AZ80D-T6 magnesium alloys are investigated by electronic universal tensile machine and with Nd: glass laser with the wavelength of 1064 nm and pulse width of 20 ns. The results show that after LSP, the tensile strength of AZ80-T6 and AZ31 alloys are increased by 4.6% and 15.7%, the surface hardness are increased by 22.7% and 31.8%, respectively. The strengthening effect of LSP on AZ31 is more significant than AZ80D-T6. The LSP generates high value residual compressive stress and high-density twins as well as the lamellar or short columnar or dynamic precipitation b phases. The grains are refined and the ultrafine grains are formed. The effect of pre - aged β precipitates on LSP strengthening effect and tensile fracture characteristics are discussed.