Monitoring the temperature of a computer server room is a critical task to ensure the performance of the server is not disturbed by excessive room temperature. In this paper, we designed and implemented a microcontroller-based room temperature monitoring system using Atmel ATmega8535 microcontroller and National Semiconductor's LM35 temperature sensor. The system is equipped with a Wavecom GSM modem to send and receive text message (SMS) and relay board to control electronic equipment. The experiment results show that our system works as expected. The system raises an alarm and send an alert message to administrator when the room temperature is above threshold, which is 28C.