The phenylalanine ammonia lyase (PAL) cDNA was amplified from Petroselinum crispum RNA by using the RT-PCR technique. The amplified 2.2 kb DNA fragment was sequenced and inserted into expression vector pET23b. The resulting plasmid pET23bPAL was then transformed into E. coli JM109DE3. The expressed PAL protein in JM109DE3 (pET23bPAL) accounted for more than 15% of total proteins in the engineering E. coli cells. The activity and specificity of the expressed PAL was identified and tested by using HPLC technique. The results indicated that the PAL activity was good enough for application to enzymatic therapy of phenylketonurea (PKU).