Metal nitrides nanosheets possess remarkable physical and chemical properties such as high electrical conductivities, catalytic properties, energy storage, and conversion efficiency. In this paper, molybdenum nitride (Mo5N6, MoN, and Mo2N) nanosheets were synthesized by nitriding and exfoliating the bulk 2H-MoS2 via dropping N from ammonia at high temperature. Molybdenum nitride nanosheets with the thickness of dozens of nanometers were prepared successfully under different conditions. It was found that the reaction between MoS2 and NH3 began from about 696 degrees C, and reduction products and reaction mechanisms were strongly dependent on the temperature. When there was MoS2, the generated Mo5N6, MoN, and Mo2N can exist stably at even 820, 1020, and 1120 degrees C, respectively. However, they will decompose progressively after MoS2 was consumed completely: at 820 degrees C, Mo5N6 started to decompose to -MoN; at 1020 degrees C, the phase evolution process of MoN can be described as follows: -MoN -Mo2N -Mo2N Mo, while at 1120 degrees C, the -Mo2N will transform to Mo.