After testing some factors such as stomata, sugar content and the activities of peroxidase(POD) polyphenoloxidase (PPO) etc. from vary ridgegourd (Luffa acutangula ) varities with differenthardiness, the results showed that in leaves of ridgegourd, the PPO ratio of reducing sugar content to totalsugar content and the stomata density of its lower epidermis were negatively relevant to its resistance a-gainst downy mildew (Pseudopronospora cubensis ). The corelation coefficients were 0. 986 1, - 0. 716 5and - 0.969 2 respectively, while the total sugar content were positively relevant to its resistance (r =0. 911 5 ). However POD activity, reducing sugar content and stomata size were all irrelevant to the resis-tance.