The treatment of muskmelon cultivar “Wangwenxiang”, which is sensitive to watermelon mosaic virus-2 (WMV-2), with oxalate increases systemic resistance of the cultivar to WMV-2 significantly. The challenge inoculation experiments indicate that the symptom of oxalate-treated plant is much slighter than that of control plants and the virus content is only 4% of that of control plants. The peroxidase activity of oxalate-treated plant is six times of that of control plants; three new isoperoxidases are induced and lignin content increases by 82.9%. These results indicate that oxalate induces systemic resistance of muskmelon to WMV-2 while it induces increase of peroxidase activity.