With computer analysis of the adenosine deaminase (ADA) mRNA, which included cleavage site selection, secondary structure analysis, biological function and homology analysis of the gene fragment around the cleavage site，four hammerhead ribozymes were designed. These ribozymes targeted sequence around the cleavage site have hairpine structure in which the cleavage site is in the ring part. This gene fragment is of biological importance in ADA gene. No homologies were found between these gene fragments and other murine genes. These characteristics of the gene fragment make them easy to be paired and cleaved by their respective ribozymes.