【Objective】To study gene expression and enzyme activities of polyphenol oxidase (PPO) from periwinkle（Catharanthus roseus）infected by Candidatus Liberibacter asiaticus.【Method】The gene fragment of periwinkle PPO (PwPPO) was obtained using PCR technique. Primers were designed according to the sequence similarity of PPO genes from different species. Expression and enzyme activities of PwPPO were analyzed in leaves, center stems and roots of C. roseus infected by Ca.L. asiaticus at different days after inoculation using qRT-PCR and physiological and biochemical methods. 【Result】The expressions of PwPPO were upregulated 4.23, 12.64 and 33.80 fold respectively in leaves, center stems and roots at 30, 35 and 40 days after inoculation. The time and extent of the upregulated expressions of PwPPO in different tissues were different. The PPO activities in leaves, center stems and roots of periwinkle infected by Ca. L. asiaticus were 2.87, 2.10 and 1.89 times respectively of healthy control at 30, 35 and 45 days after inoculation respectively. 【Conclusion】Gene expression level of PwPPO is proportional to PPO activity, and is related closely to the resistance ability of host periwinkle against Ca. L. asiaticus invasion.