This study investigates the thermal kinetics and nitriding effect of ammonia-based direct reduction of iron oxides. The research focuses on understanding the reaction kinetics under different process conditions and the associated nitrogen incorporation in the reduced material, which originates from ammonia decomposition. The effects of temperature on reduction efficiency and nitride formation are explored through phase, local chemistry, and gas evolution analysis. The study also examines the impact of inherent reactions and diffusion on phase formation and chemistry evolution, as well as the nitrogen incorporation through spontaneous and in-process nitriding. The reoxidation tendency of the ammonia-based reduced material is compared with that of hydrogen-based reduced material. The results provide a fundamental understanding of the reduction and nitriding processes for iron oxides exposed to ammonia at temperatures from 500 to 800 °C, serving as a basis for the exploitation and upscaling of ammonia-based direct reduction for future green steel production.This study investigates the thermal kinetics and nitriding effect of ammonia-based direct reduction of iron oxides. The research focuses on understanding the reaction kinetics under different process conditions and the associated nitrogen incorporation in the reduced material, which originates from ammonia decomposition. The effects of temperature on reduction efficiency and nitride formation are explored through phase, local chemistry, and gas evolution analysis. The study also examines the impact of inherent reactions and diffusion on phase formation and chemistry evolution, as well as the nitrogen incorporation through spontaneous and in-process nitriding. The reoxidation tendency of the ammonia-based reduced material is compared with that of hydrogen-based reduced material. The results provide a fundamental understanding of the reduction and nitriding processes for iron oxides exposed to ammonia at temperatures from 500 to 800 °C, serving as a basis for the exploitation and upscaling of ammonia-based direct reduction for future green steel production.