We have been conducting a mouse cDNA project to predict protein-coding sequences of mouse homologues of human KIAA and FLJ genes since 2001. As an extension of these projects, we herein present the entire sequences of 500 mKIAA cDNA clones and 4 novel cDNA clones that were incidentally identified during this project. We have isolated cDNA clones from the size-fractionated mouse cDNA libraries derived from 7 tissues and 3 types of cultured cells. The average size of the 504 cDNA sequences reached 4.3 kb and that of the deduced amino acid sequences from these cDNAs was 807 amino acid residues. We assigned the integrity of CDSs from the comparison with the corresponding human KIAA cDNA sequences. The comparison of mouse and human sequences revealed that two different human KIAA cDNAs are derived from single genes. Furthermore, 3 out of 4 proteins encoded in the novel cDNA clones showed moderate sequence similarity with human KIAA proteins, thus we could obtain new members of KIAA protein families through our mouse cDNA projects.