1) In the present experiment, the pollinator association in the Japane pear, Purus serotina Rehider var. Nijisseiki orchard on the flowering period was investigated at 15th to 27th April, 1975.
2) The collected insects as pollinator are as follows ; Andrenidae : eleven species, Halictidae : two species, Apidae : three species, and Syrphidae : eight species.
3) The structure of pollinator association in hymenopterous insects showed the most complexity at 09.00 hr, and that in dipterous insects showed the most complexity at 12.00hr.
4) The similarity of structure among the associations was examined by the method of index of overlap degree. The index of degree of overlap in andrenid bees association was low 17.00 hr vs. the other times. In syrphid flies association, the index of overlap degree on each hour was low in 09.00 hr vs. 10.00 hr and in 10.00hr vs 16.00 and 17.00 hrs.
5）The main species in pollinator association collected at 09.00-15.00, 16.00 and 17.00 hrs was Eristaliscerealis, Andrena sp. and Lassioglossum sp.(1), respectively.
6）It can be concerned that the main species of pollinator in the Japanese pear, var. Nijisseiki orchard at San-In District are six species as follows ; Andrenidae : Andrena sp., Andrena foveopunctata, Andrena benefica and Andrena kaguya, Syrphidae : Eristalis cerealis and Helophilus virgatus.