- In multi-access network environments, interworking technologies has become a very important issue these days. This interworking would deliver optimized services to users and also benefit service providers by reducing network construction and maintenance costs. This paper proposes a cost-effective scheme for fast handoff between mobile WiMax and cdma2000 networks. The smoothly integration scheme proposed in this paper adopts the advantages of both loosely integration and tightly integration schemes: cdma2000 and Mobile-WiMax networks provide their own services independently and, on vertical handoff between them, support seamless services by fast handoff. Since we present protocol stacks as well as operation flows considering cdma2000 and Mobile-WiMax standard specifications, the proposed scheme can be implemented with minimal modification of existing MobileWiMax and cdma2000 networks. As result of simulation, we proved performance of the proposed scheme compared with others. Key words...