This project is aimed to design a system to control the electrical appliances in home/office by using GSM technology. A GSM modem provides the communication interface. It transports device protocols transparently over the network through a serial interface. A GSM modem is a wireless modem that works with a GSM wireless network. This GSM Modem can accept any GSM network operator SIM card and act just like a mobile phone with its own unique phone number. Advantage of using this modem will be that you can use its RS232 port to communicate and develop embedded applications. Applications like SMS Control, data transfer, remote control and logging can be developed easily. The modem can either be connected to PC serial port directly or to any microcontroller. This project is designed in such a way that a GSM modem is interfaced to the controller through serial port interface, along with the AC devices/loads which are to be controlled by using GSM will be interfaced to the controller through the relays. The GSM modem performs the task of receiving the message from the mobile and sending the messages to the mobile from the controlling unit. If the user wishes to control the appliances ON/OFF in home/office, he has to send a predefined message to the modem from his mobile. The GSM modem receives this message and intimates the same to the microcontroller. Now it is the job of the controller to switch ON/OFF the corresponding appliances in accordance with the received message. A 16X2 LCD will be interfaced to the controller to display the status of the appliances. This project uses regulated 5V, 500mA power supply. Unregulated 12V DC is used for relay. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac output of secondary of 230/12V step down transformer.