Wireless sensor network (WSN) consist of a large number of sensor nodes which are limited in battery power and communication range and are having multi-modal sensing capability. One of the most significant applications of wireless sensor network is environment monitoring. In this paper, a multi-sensor data fusion algorithm in WSN using fuzzy logic for event detection application is proposed. In the proposed method, each sensor node is equipped with diverse sensors (temperature, humidity light, and carbon monoxide). The use of more than one sensor provides additional information on the environmental condition. The processing and fusion of these diverse sensor signals are carried out using proposed fuzzy rule based system. All the diverse sensor signals are collected at the cluster head and fused using fuzzy rule based method. The multiple data fusion process improves the reliability and accuracy of the sensed information and thereby minimizes the false alarm rate.