In this paper the controlling mechanism for monitoring the environmental factors inside a polyhouse is proposed. By using this technique the ambient temperature and humidity can be controlled. These two factors are crucial for the plant growth inside a polyhouse. The prototype is designed by using AT89S52 microcontroller and tested successfully. The system can provide ideal temperature and humidity values as required for the proper growth of the plant. Using the GSM module the farmer can check the temperature inside the polyhouse from a remote location and based on the preloaded temperature values the motors and fans provide sufficient cooling and humidity inside the polyhouse. The advantage of this system lies in reducing the human effort by automation which further provides suitable environment inside the polyhouse. The installation cost is considerably less for the proposed system. For monitoring temperature inside the polyhouse LM35 temperature sensor is used because of its accuracy and fast transmission of data. SY-HS-220 humidity sensor is used for monitoring the humidity inside the polyhouse. These two sensors are integrated with the microcontroller through MCP3208Analog to digital converter. Whenever the temperature and humidity inside the polyhouse increases beyond 25°C, the motor and the fan are turned on automatically to cool the temperature, which are connected to the microcontroller by L293D. The same information about the status of temperature, humidity and motors is transmitted to the farmer and PC node through GSM Module via MAX232. Keil uVision4 cross compiler has been used for implementing the proposed system.