Handoff is one of the most important factors that may degrade the performance of TCP connections in wireless data networks. In this paper, we present a lossless and duplication free handoff scheme called LPM (Last Packet Marking) for improving Cellular IP semisoft handoff. LPM signals the safe handoff cue by sending a specially marked packet to mobile hosts. With this control packet, MH can adapt to network dynamics simply and efficiently. Our performance study shows that LPM achieves lossless packet delivery without duplication and increases TCP throughput significantly. Keywords Micro Mobility, Cellular IP, Hard Handoff, Semi-soft Handoff, Last Packet Marking