As a part of ecological studies on Haemaphysalis longicornis, the effects of controlled temperatures (12, 15, 20, 25 and 30 degrees C; approximately 100% RH) on development and growth of the tick were investigated and the critical low temperature for each stage in the life cycle was estimated. As the temperature became low, the periods of preoviposition, oviposition, egg hatching (incubation) and moulting were prolonged. At 12 degrees C, however, oviposition, egg hatching and moulting of the larva and nymph did not occur. The critical low temperatures for oviposition, egg hatching (developmental zero) and larval and nymphal moulting, which were calculated theoretically from the regression equations, were 11.1, 12.2, 10.2 and 11.8 degrees C, respectively. The temperature also affected the egg productivity and hatch-ratio. The number of deposited eggs per mg of body weight decreased markedly at 15 degrees C, and the hatch-ratio was lowered with dropped temperatures.