Abstract Metal injection molded (MIM) 17-4 PH stainless steels are wildly used in the aircraft and medical industries due to the good mechanical properties and corrosion resistance. The 17-4 PH stainless steel is typically sintered in the dual phase region of δ+ γ under vacuum or hydrogen. Since nitrogen provides solution strengthening and dissociated ammonia (DA) is widely used in continuous furnaces in the industry, the 17-4PH was sintered in DA in this study and its effect on mechanical properties and corrosion resistance was investigated. Results showed that when the 17-4 PH was sintered in vacuum or hydrogen at 1320℃, 97.0% density was achieved, higher than the 94.3% of that sintered in DA. This was because the amount of delta ferrite is about 61% in hydrogen but only 38% in DA. By increasing the sintering temperature to 1350℃ or adding 1 wt% Mo into 17-4 PH, the amount of delta ferrite increased to 56% and 57%, respectively. Thus, high sintered density was attained. Specimen sintered in DA at 1350℃ reached 45.7 HRC hardness and 1350 MPa tensile strength, which are much higher than those of sintered in vacuum and hydrogen at 1350℃. However, the elongation and impact energy of the specimen sintered in hydrogen or DA were very low, around 4% and 6J. The corrosion resistance of 17-4 PH sintered in DA was poor at a rate of 0.0160 g/dm2/day, which exceeded the MPIF limit. To improve the properties of the 17-4PH sintered in DA, 1 wt% Ni was added into 17-4 PH. A hardness of 39.7 HRC, a tensile strength of 1365 MPa, an elongation of 6.4%, and an impact energy of 43.6 J was attained after solutioning and aging treatment. On other hand, when 15 wt% 316L was added into 17-4PH, the hardness, tensile strength, elongation, and impact energy were 36.6 HRC, 1264 MPa, 12.2%, and 64.7J was attained after solutioning, cryogenic, and aging treatment. Both these two methods decreased the hardness after solution treatment to 25.4 and 21.5 HRC for the specimen added with 1 wt% Ni and 15 wt% 316L, respectively. This hardness range is good for machining. The corrosion resistance was also improved by adding Ni and 316L addition. The weight loss rates of the specimens with the addition of 1 wt% Ni and 15wt% 316L were decreased to 0.0089 and 0.0044 g/dm2/day, respectively, after heat treatment. Keywords: Metal injection molding, 17-4 PH stainless steel, aging treatment, cryogenic treatment