Abstract. Vertical partition is an important technique in database design used to enhance performance in database systems. Vertical fragmentation is a combinatorial optimization problem that is NP-hard in most cases. We propose an application and an adaptation of an improved combinatorial particle swarm optimization (ICPSO) algorithm for the vertical fragmentation problem. The original CPSO algorithm [3] suffers from major drawback—redundant encoding. This paper applies an improved version of CPSO that using the restricted growth (RG) string [5] constraint to manipulate the particles so that redundant particles are excluded during the PSO process. The effectiveness and efficiency of the improved CPSO algorithm are illustrated through several database design problems, ranging from 10 attributes/8 transactions to 50 attributes/50 transactions. In all cases, our design solutions match the global optimum solutions.