Compressed natural gas (CNG) fuel has recently gained popularity in passenger and commercial vehicles due to its lower cost of operation compared to gasoline and diesel. It is also a more environmentally friendly fuel than other fuel. Converting a customer vehicle (with a diesel option) to the CNG option is more difficult than building a new CNG vehicle. In this we are outlining the design of CNG fuel systems and the challenges of replacing them during the transition from Diesel to CNG and qualifying the Government Norms for running the vehicle will increase the life as well as make our environment more eco-friendly than Diesel Vehicle. Using CNG as a fuel in the automotive industry gives benefits over Gasoline & Diesel • increased life of lubricating oils, as CNG does not contaminate and dilute the crankcase oil. • Lower cost of per unit energy. • Being a gaseous fuel, CNG mixes easily and evenly in air, hence less hazardous. • CNG is less likely to ignite on hot surfaces, since it has a high auto-ignition temperature (540 °C), and a narrow range (5-15 percent) of flammability. • CNG emits significantly less pollution directly than gasoline or diesel when combusted (e.g., unburned hydrocarbons (UHC), carbon monoxide (CO), nitrogen oxides (NOX), sulphur oxides (SOx) and PM (particulate matter). Keywords: Diesel, CNG, Commercial Vehicles, Converting, Eco-Friendly.