Provided is a method of determining an operation mode of a node in an ad hoc network. The method includes: monitoring a measured amount of residual energy of the node and comparing the measured amount of residual energy of the node with an amount of residual energy theoretically calculated for the node; identifying an amount of information in a queue included in the node; calculating a relay probability of the node by reflecting the identified amount of information in the queue and the result of comparing the measured amount of residual energy of the node with the theoretically calculated amount of residual energy for the node; and determining the operation mode of the node to be one of a relay mode and a transmission mode, based on the calculated relay probability of the node. The method enables nodes to exchange information about their respective amounts of residual energy and analyze the information without using additional resources and processes.