In search of the attractant in rice grains for rice weevils, an olfactometer was devised. That was a modified Chamberlain's cage type olfactometer and suitable for bioassay for the attractancy of rice grains and the extract or fractions from the rice grains. The bioassay was conducted at 25-30 degrees C under darkness and 14-16% relative humidity, with 50 rice weevils that had been starved and cut water supply for 2 days prior to the test. This method gave good results for detecting the presence of attractive material in the sample.