Compressed Natural Gas (CNG) has been applied worldwide for in-used engines, especially CNG engines that are converted from the conventional engines. However, it encounters the problem related to the low power and high fuel consumption of the conventional engine fueled by CNG. This paper presents an experimental study on performance enhancement of a CNG engine converted from the spark-ignition engine by the implementation of fuel additive Maz 100. In experimental work, a fuel additive supplying system was developed to impose a certain amount of fuel additive to the intake manifold of the test engine. The study results show that when using Maz 100, the brake power of the test engine improves approximately 6.75% on average at full load conditions. The brake specific fuel consumption (BSFC) reduces 6.49% on average at full load and 3.53% on average at partial load condition. In addition, besides the benefit of performance enhancement, exhaust emissions of the test engine in the case of operating with fuel additive have changed considerably. Particularly, the CO emission reduces 36.1% at full load and 18.4% on average at partial load conditions. The HC emission reduces 37.1% at full load and 35.0% on average at partial load conditions. The NOx emission increases slightly in low-speed regimes and reduces in high-speed regimes when the engine operates at the full opened throttle condition. At partial load condition and speed of 3000 rpm, the NOx emission reduces 22.6% on average. Implications: This paper presents a solution for performance enhancement and emission reduction of natural gas engine by using fuel additive. Performance and emission characteristics of the natural gas engine fueled with fuel additive have been assessed in the laboratory. The performance of the test engine improves remarkably. The brake power of the test engine improves approximately 6.75% on average at full load conditions when the engine operates with fuel additive. The brake specific fuel consumption reduces 3.53% on average at partial load condition. The emission of pollution has different trends. The CO and HC emission reduces at testing conditions. The NOx emission increases slightly in low-speed regimes and reduces in high-speed regimes when the engine operates at the full opened throttle condition. The implementation of fuel additive is a potential solution for power improvement and emission reduction of natural gas engine.