Cryptanalysis is a complex and mathematically challenging field of study. It takes some data or message, which is called cipher text and attempt to restore its plaintext. This paper attempts to use an improved particle swarm optimization (PSO) to obtain the plaintext from the transposition cipher. This improved method gives a good performance for the PSO algorithm by generating best solution from the best to avoid stability to reach to solution (key). This key is used for breaking transposition cipher.