Abstract: A full-length cDNA of phenylalanine ammonia lyase-homologue（AcPAL2）was isolated from onion using degenerate PCR and the RACE（rapid amplification of cDNA ends）method. The full-length cDNA is 2 349 bp long，which encodes a polypeptide of 685 amino acids. Blast analysis indicate that the polypeptide shares a relatively high similarity with Galtonia saundersiae and Musa balbisiana. Real-time PCR analysis demonstrate that AcPAL2 mRNA express abundantly in red onions，but extremely low in yellow and white onions；AcPAL2 in different bulb swelling stage in red onion has a high expression during the initiation，then express stable after a rapid decrease. And anthocyanin content change also shows the same tendency with AcPAL2 expression.