The present paper examines the use of natural gas in a small four-stroke engine of internal combustion, which is used for the movement of a small alternative generator. The electrical generator functioned without load and under different loads (500, 1000, 1500 and 2000 W), using as fuels gasoline and natural gas. During the tests, it has been observed the CO and HC emissions for every fuel and load condition. The use of natural gas as fuel has as a result the CO and HC emissions decrease under different load. The flow of natural gas was regulated so that until the load of 2000W the behavior of the engine from the aspect of efficiency to be the same with that of gasoline. This means that the engine rpm was the same for every electrical load in both fuels gasoline and natural gas. During the tests, the consumption of gasoline and natural gas were recorded and it has been noticed that they were increased when the electrical load was increased too. As far as the consumption of natural gas is concerned, it has been noticed that it gives the same behavior of the engine from the aspect of power and engine rpm that the manufacturer gives for the use of gasoline.