Abstract: A method for updating firmware of a plurality of nodes constituting a wireless sensor network is disclosed. The wireless sensor network includes a server, a gateway and the plurality of nodes. The firmware to be updated is transmitted from the server through the gateway to an uppermost node. The firmware is sequentially transmitted to the plurality of nodes from the uppermost node to a lowermost node using wireless communication, and the respective nodes, which have received the firmware, record the firmware in their own memory. When the recording of the firmware is completed in all the nodes, boot programs of the respective nodes are run and the firmware, stored in the memory, is recorded in program memory, the firmware recorded in the nodes are executed, and the nodes constitute a new network while communicating with the peripheral nodes thereof.