There have been many wireless sensors equipped IEEE802.15.4. ZigBee, the most representative upper layerprotocol of IEEE802.15.4 is non-IP-based. However an IPv6 protocol called 6LoWPAN is currently being discussed by the IETF Until now, IP stacks have generally been too large for sensor devices, which have weak calculating ability. Thus, most of wireless sensor networks are non-IP networks. The Internet, of course, generally are using IP. If we can use IP with wireless sensor networks, we can reap the benefits of the IP's superior technology. Researches in this field aim to develop wireless sensor networks using IPv6 and obtain the efficiency of IP-capable wireless sensor networks. However, problems with the buffer overflow have been reported in some implementations of 6LoWPAN. In this paper, we propose a memory buffer control mechanism for 6LoWPAN, and evaluate an implementation of a 6LoWPAN protocol stack using this mechanism. Results of this implementation have shown that the buffer control mechanism worked efficiently.