Abstract: The diel rhythm of the sex pheromone titre in the pheromone glands of one day old vergin females was found to be in a two peak curve by bioassay. The two peaks were at 2:00~6:00 and 17:00-20:00, the titre of the latter was approximately 100 times higher than that of the former. The diel rhythm of the carbon dioxide exhalation and the heart beat were also determined to show curves similar to that of the sex pheromone. The peak periods of these physiological activities coincided with the calling behaviour and mating activities of Clania variegata in forests.The relation between the number of heart beats and the rate of releasing pheromone by a vergin feemale at the calling time was determined by bioassay. The regression equation Y = 40.20 + 1.18X was constructed, where Y is the releasing rate (rndicated by the male response percentage) and x is the heart beats (bonts/ min.), The average rate of sex pheromone releasing by a single one day old female in its calling time 17:00-20:00 was calculated to be 0.012 FE/min. This means that the glands of the female only contained the amount of pheromone which was going to be released during the same calling period, i. e. pheromone synthesizing and releasing occured simultaneously.Based upon the analyses on the diel physiological rhythms, the mechanism of releasing sex pheromone in Clania variegata is suggested: During the calling time the metabolism of the vergin female was speeded up and the energy released was mainly used for increasing the heart beats and the blood pressure, which forced the pheromone synthesized in the gland cells to burst out of the insect’s body from the end apparatuses through the canals to its pores on the cuticle.