Background : Acreage of rain-shelter plastic greenhouse to prevent anthrax is being gradually increased according to growing importance of safe Boxthorn production. But When Boxthorn is grown in the hot season in rain-shelter plastic greenhouse, Fertility decreases. The fertilization rate tends to be different according to cultivated variety and ventilation type of rain-shelter plastic greenhouse. Therefore it is necessary to identify cause and look for a solution. Methods and Results : In the experiment, ‘Cheongun’ cultivar was grown in the rain-shelter plastic greenhouses for the tests. Environment of rain-shelter plastic greenhouses, fertilization rate and density of flower visiting insect were investigated according to ventilation type. Pollen germination and pollen tube elongation on stigma were investigated according to temperature. In mid-July, the temperature on a clear day rose to 45℃ in rain-shelter plastic greenhouse of side vents. Pollen germination and pollen tube elongation on stigma were normal for 3 hours on 30, 35℃. Fertilization rate was somewhat reduced on 40℃ but Pollen germination and pollen tube elongation was good. On 45℃, fertilization rate was very poor and There was no pollen germination. Density of flower visiting insect in rain-shelter plastic greenhouse of roof and side vents was higher than that in rain-shelter plastic greenhouse of side vents. The fertilization rate on high temperature did not show any difference regardless of ventilation type. The rate of artificial cross-fertilization and airborne fertilization were high in rain-shelter plastic greenhouse of roof and side vents. It was necessary to improve airborne fertilization rate because airborne fertilization rate was significantly lower than artificial cross-fertilization regardless of ventilation type. Conclusion : When it was cultivated in rain-shelter plastic greenhouse, the reasons for the lowering of the fertilization rate were as follows. Density of flower visiting insect was low. Boxthorn, which was insect pollination crop, was needed sufficient flower visiting insect on flowering period. But it was insufficiency especially in rain-shelter plastic greenhouse of side vents. Another reason was decrease in pollen germination and pollen tube elongation. Pollen germination was suppressed in the high temperature.