This work presents the design and simulation of a microcontroller based under and over voltage protection device, which has been achieved using a microcontroller, transistor and other discrete components. A microcontroller is at the heart of the device which performs the major control of the device. The device is simple and low cost. It can withstand loads up to 2KVA at the required set voltage range for the device, to allow supply to the connected load at the output vary from 200 – 240 Volts. It can be used to protect loads such as refrigerators, radio sets, laptops and VCR/DVD players etc. from undesirable over and under voltage conditions, as well as surges caused due to sudden failure/resumption of mains power supply. This device can be used directly as stand-alone equipment between the mains supply and the load, or it may be inserted between an existing automatic/manual stabilizer and the load.