Provided are a sensor node included in a sensor network, an update server updating the sensor node, and a method of updating a sensor node. The update server updating a sensor node included in a sensor network includes an execution code manager managing execution codes for a plurality of sensor nodes included in the sensor network, a rule generator generating an update rule based on a result of comparing an existing execution code managed by the execution code manager with an update execution code required for a new function update of the sensor node, and a downloader causing the sensor node to download the update rule generated by the rule generator. Accordingly, an execution code can be updated by a small amount of data transmission.