Density and sintering temperature effects were investigated with FL4405 low alloy P/M high strength steel. Monotonic tensile stress-strain, plane strain fracture toughness and fatigue behavior of smooth, notched and cracked specimens were investigated under both constant and variable amplitude loading. Two density levels, 7.0 and 7.4 g/cm3 and two sintering temperatures, 1120 and 1315‡C, were evaluated. The increased density resulted in smaller pore size and pore volume and the increased sintering temperature resulted in greater pore roundness. All final fracture surfaces were brittle at the macro level while containing ductile dimples at the micro level. Fatigue surfaces contained cleavage only, ductile dimples only or mixed cleavage and ductile dimple morphology with no striations nor beachmarks. Increasing the density resulted in significant higher tensile strength, elastic modulus, ductility, fracture toughness and fatigue resistance. Increasing the sintering temperature, and hence increasing pore roundness, resulted in additional enhancement of these properties. However, this increase was not as significant as that of the density increase.