When the temperature of the combustion chamber rises beyond 1800 K in internal combustion engines, the nitrogen and oxygen in the air combine chemically and become a gas called nitrogen oxide, which is harmful to human health and the environment. Nitrogen oxides combine with humidity in the lungs and become nitric acid, which causes breathing illnesses. Diesel engines use excess air for combustion, and this increases nitrogen oxide production potential. In this research, the reduction of nitrogen oxide emissions from diesel engines was investigated. For this purpose, a single cylinder diesel engine's exhaust gases were recirculated to the engine induction system at determined rates (10, 20, 30%) and changes in engine performance and exhaust emissions were traced. The results show that nitrogen oxide emissions decreased drastically but smoke emissions and specific fuel consumption deteriorated.