—Wireless sensor networks are often composed of resource-constrained sensor nodes with limited memory space, computational capacity and communication range. The links in WSN are often lossy and unreliable. In order to make fluent and reliable data transport on memory-constrained sensor nodes, we propose a new transport layer protocol Reliable Transport with Memory Consideration(RTMC), which provides both hop-by-hop retransmission and congestion control. We have implemented RTMC on MICA2 with only 4K bytes RAM. Experiment, analysis and simulation results show that RTMC can use channel resource effectively and enable all of the segments to be received by the sink with low transport time and low memory cost.