Growth parameters (seedling elongation, fresh and dry masses) and protein content of Cucumis melo were enhanced by juglone (allelochemical occuring in the walnut family) treatment in pregerminative stage but decreased in postgerminative treatment. Catecholase and tyrosinase activities were also increased in both treatments. Xylem vessel radius of stem was enhanced significantly by the pregerminative treatment, whereas it decreased slightly by the postgerminative treatment. However, bundle radius of stem was enhanced by both treatments of juglone. Stomata length and number were not changed significantly. Xylem vessel radius of the stem was affected by juglone more than the other parameters.