Thin films of molybdenum nitride and tungsten nitride were deposited by metal organic chemical vapour deposition (MOCVD) employing the mixed amidinato-imido compounds [M(N^tBu)₂{(ⁱPrN)₂CMe}₂] (M=Mo (1), W (2)) as potential precursors under single source precursor (SSP) condition and in the presence of ammonia at substrate temperatures of 500°C-800°C. Under SSP conditions, the films consisted of the nitride and carbide phases for both the material systems, while the addition of ammonia during the MOCVD process led to the formation of the respective metal nitrides. The films were smooth and amorphous at 500°C, and comprised of very fine grains at higher temperatures. Elemental composition investigated by complementary techniques such as Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) and X-ray photoelectron spectroscopy (XPS) revealed that the films grown in the presence of ammonia had increased levels of nitrogen and decreased carbon content relative to films grown under SSP condition.