Abstract: Infection of periwinkle (Vinca rosea) with paulownia witches' broom agent (mycoplasma like organism) by dodder resulted in regular changes in peroxidase isoenzymes. Peroxidases of leaves and stems in the healthy periwinkles were separated into 11 bands at most, generally 6 bands including Ⅰb、Ⅰc、Ⅰd, Ⅱ、Ⅲd and Ⅲe by polyacrylamide gel electrophoresis (PAGE). 4 band visible were shown in the infected plants with typical symptoms of yellow leaves, witches' broom and phyllody while band Ⅲd and Ⅲe (with lower Rf value than other bands) could not be detected. It was confirmed that the concentration and width of band Ⅲd and Ⅲe have close relation to the symptoms of periwinkle infected with PWB-MLO and ages of periwinkle. The healthy seedlings with less than 7 pairs of leaves were also lack of band Ⅲd and Ⅲe. The root immersion of diseased plants in oxytetracycline solution could make symptoms subside partially, and the result of PAGE of peroxid-ases showed that the concentration and activity of band Ⅲd and Ⅲe in the treated plants were higher than the control (root immersion in distilled water) but still lower than the healthy plants (root immersion in oxytetracycline or distilled water). We deduced that the presence of band Ⅲd and Ⅲe of peroxidase isoenzymes is a good indicator of the resistance of periwinkle against PWB-MLO.