Protected Horticulture Research Institute, NIHHS, RDA, Haman, 637-812, KoreaReceived on 23 October 2015, revised on 8 December 2015, accepted on 21 December 2015Abstract : The ventilation systems composed three types of side vent (roll-up) ‘SV’, side vent+roof vent ‘SV+RV’, and side vent+roof fan ‘SV+RF’ with 7.5 m spacing, with specific set point temperatures for ventilation: SV (35℃ open / 33℃ close), SV+RV or SV+RH (35℃ open/33℃ close for root ventilation and 37℃ open / 35℃ close for side vent). In the treatment of SV+RV, although the average daily maximum temperature inside the greenhouse temporarily increased by 38 - 40℃, thermal stress by high temperature did not occur and the disease incidence (%) of powdery mildew and downy mildew on the oriental melon were 25 - 75% lower than in the conventional SV treatment. In the SV treatment, the disease incidence (%) of powdery mildew and downy mildew were 1.4 - 7.7% and 4.2 - 15.9% for ‘Deabakkul’,and 20.3 - 22.8% and 2.8 - 11.3%, for ‘Ildeungkkul’. The yield for one month was higher in the treatment of SV+RV than those in other treatments, with values of 2,105 kg/10a for ‘Deabakkul’ and 2,537 kg/10a for ‘Ildeungkkul’. The simultaneous treatment with side vent and roof vent resulted in 16.2% higher yield (18.1% higher marketable yield) than that in the SV treatment for ‘Deabakkul’.Key words : Oriental melon (Cucumis melo L.), Single-span plastic greenhouse, Side vent, Roof ventilation, Roof vent, Roof fan, disease incidence (%)*Corresponding author: Tel: +82-55-580-5533E-mail address: khyeo@korea.kr