Multimedia object caching, by which the same multimedia object can be adapted to diverse mobile appliances through the technique of transcoding, is an important technology for improving the scalability of web services, especially in the environment of mobile networks. In this paper, we address the cache replacement problem for multimedia object caching by exploring the aggregate effect of caching multiple versions of the same multimedia object. First, We present an optimal solution for calculating the minimal access cost of caching multiple versions of the same multimedia object. Second, based on this solution, we propose an effective cache replacement algorithm for multimedia object caching. Finally, we evaluate the performance of the proposed solution with a set of simulation experiments for various performance metrics over a wide range of system parameters. Key words: Web caching, multimedia, cache replacement, transcoding, optimization, Internet.