High pressure die cast magnesium alloy AM50 is currently used extensively in complex shaped automotive components with various cross-section thicknesses. Understanding of the effect of section thicknesses on mechanical behavior of AM50 is critical for proper design of different applications. In the present study, magnesium alloy AM50 was high pressure die cast into rectangular coupons with section thicknesses of 2, 6 and 10 mm. The prepared coupons were tensile tested at room temperature. Microstructure analysis and porosity measurement were performed on the representative specimens. The results of tensile testing show that the tensile properties including yield strength (YS), ultimate tensile strength (UTS) and elongation(E(f)) decreases with an increase in section thicknesses of die cast AM50. Microstructure and porosity analyses indicate that the observed tensile behavior of die cast AM50 is primarily attributed to the level of porosity which resulted from entrapped gases during the high pressure die casting process.