Wind energy is one types of renewable energy and it does not cause pollution. Therefore, presently, there is the technological development of applying wind energy for the electricity generation. Wind energy is used to replace fossil energy such as oil and coal, causing environmental pollution. Moreover, Thailand has promoted the studies of wind energy application to generate electricity. Nowadays, there is number of small and medium wind turbines used for electricity generation for buildings, houses and small communities. Since Thailand is located in the tropical climate, the buildings, houses and industrial facilities prefer installing roof ventilators to vent hot air out of the roof. Therefore, the author proposed the roof ventilator system equipped with a small direct current electric generator. A 18-watt DC generator was installed in 24-inch roof ventilator and carry around rotation of the generator by gear to the rotation axis of roof ventilator. The results of the study were found that roof ventilator would begin to generate a voltage of 0.2 - 0.3 volt at wind speed of 0.5 meters per second. When the wind speed is higher than 2 meters per second, it would produce about 3.5 volts. However, when connecting the voltage produced by the generator to the DC Step-Up Converter, it was found the wind speed of 5 meters per second. DC generators can produce a voltage of 3 volts. With the DC Step-Up Converter, the voltage would increase to approximately 12 volts and can the current to 220mA, which is sufficient level to work with light-emitting diode lamp. In sum, the system of roof ventilator with a small DC generator could be applied to generate electricity for various households.