The object of this research has been to determine the effects of both variations in sintering time at 1150°C and in subsequent heat-treatment conditions on the final mechanical properties and microstructure of sintered low alloy steels containing 1.5% copper, 1.75% nickel and 0.5% molybdenum made from diffusion bonded partially prealloyed iron powder with additions of zero, 0.3% and 0.5% carbon. The effects of variations in porosity content on the mechanical properties of these sintered low alloy steels also has been examined using samples containing 6% and 15% porosity.