Abstract 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 (Mo 5 N 6 , MoN, and Mo 2 N) nanosheets were synthesized by nitriding and exfoliating the bulk 2H‐MoS 2 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 MoS 2 and NH 3 began from about 696°C, and reduction products and reaction mechanisms were strongly dependent on the temperature. When there was MoS 2 , the generated Mo 5 N 6 , MoN, and Mo 2 N can exist stably at even 820, 1020, and 1120°C, respectively. However, they will decompose progressively after MoS 2 was consumed completely: at 820°C, Mo 5 N 6 started to decompose to δ‐MoN; at 1020°C, the phase evolution process of MoN can be described as follows: δ‐MoN→ γ‐Mo 2 N→ β‐Mo 2 N→ Mo, while at 1120°C, the β‐Mo 2 N will transform to Mo.