Most human feels inconvenient about changing the fan speed level manually when the room’s temperature changed. So, the automatic fan system that automatically changes the speed level according to temperature changes is recommended to be built for solving this problem. Hence, the objectives for this project are to enable the electric fan to automatically change the speed level according to temperature changes and develop an automatic fan system that can change the speed level due to the environment temperature changes. This project presents the designs and the simulation of a DC fan control system based on room temperature using pulse width modulation technique and temperature sensor namely LM35 with Arduino Uno Microcontroller. The fan will be used to reduce the temperature of a room at certain level. To build the fan, we use the LM35 heat sensor. The sensor will measure the room temperature continuously. When the room temperature sensed by the sensor crossed the threshold, the value fan is switched on; the LED will be turn on. The fan will remain on till the temperature reduces below the threshold value. This general idea is used in this project.