At zoos in Japan, reindeers have been attacked by stable flies and be affected thereby. We counted the numbers of stable flies attacking reindeer at Akita Omoriyama Zoo. We sprayed 10 ml of flumethrin 1% formulation onto the limbs and abdomens of four reindeer. Before and after this treatment, we counted the number of stable flies on the reindeer, visually and via a video camera, from 10:00 to 15:00 each day. We made these observations over two periods, from August 17th to August 26th and from August 29th to September 15th. We compared the results before and after application on the formulation, using the Mann-Whitney test. In period 1, the number of stable flies on the reindeer body surfaces significantly decreased until the fifth day after application of the formulation. In period 2, the number of stable flies significantly decreased until the ninth day after application of the formulation.