The relationship between ecdysteroids (ECs) and the attractant sex pheromone, 2,6-dichlorophenol (2, 6-DCP), in female Haemaphysalis longicornis was investigated by GC and RIA separately. 2, 6-DCP firstly appeared in female foveal gland on d5 after emerged from nymph, then it increased and deposited in foveal gland and reached a peak (10.71 ng/tick) on the day just when capable of feeding. After feeding, 2, 6-DCP declined on d3 and maintained at a relatively stable level from d3 to d5. After mating, 2, 6-DCP decreased significantly and could not be detected on the day of engorgement. A peak of ecdysteroids in female whole body extracts was found on d3 after emerged from nymph. Inoculation of 20-hydroxyecdysone (20-E) on d1 newly emerged female could enhance the level of 2, 6-DCP. The above results suggested that female 2,6-DCP synthesis was regulated by ecdysteroids in this species.