A method and apparatus for estimating available throughput of a fixed node in a mobile node of a communication network. The communication network includes fixed nodes connected to a router connected to at least one foreign network and mobile nodes connected to the fixed nodes. A second mobile node is selected from among mobile nodes connected to a fixed node whose available throughput is estimated in a first mobile node. An idle slot interval of the second mobile node connected to the fixed node is set. A transmission probability is measured in one slot interval of the second mobile node through an average of set idle slot intervals. Transmission information of the second mobile node is acquired using the measured transmission probability. The available throughput of the fixed node is estimated using the acquired transmission information.