Nickel/detonated nanodiamond composites were prepared using the powder metallurgy technique. Detonated nanosized diamond particles were reinforced in the nickel matrix. The investigated powder was used to prepare homogenous diamond/nickel composite mixtures with different detonated nanodiamond content of weight percentage (0.2, 0.4, 0.6, and 0.8 wt.%). The produced mixtures were cold pressed into a cylindrical die shape under compaction pressure of 400 MPa followed by sintering at 1,000°C for 120 min under a controlled atmosphere of 1:3 hydrogen/nitrogen gas mixture. Phase identification and microstructure of the produced sintered samples were investigated using X-ray diffraction and scanning electron microscope, respectively. The results of the microstructure show a good distribution of the detonated nanodiamond in the nickel matrix, especially in the 0.8 wt% diamond/nickel sintered sample. The densities of the obtained sintered samples were measured by applying the Archimedes principal. As the detonated nanodiamond content was increased in the nickel matrix, the density of the sintered samples was decreased. The thermal expansion, electrical conductivity, and hardness of the produced diamond/nickel composites were measured. The coefficient of thermal expansion and electrical conductivity were decreased, but the hardness was increased by increasing the detonated nanodiamond weight percentage.