[Objectives]  To understand how diapause-inducing, or diapause-terminating, photoperiod and temperature influence the diapause intensity of the Asian corn borer, Ostrinia furnacalis. [Methods]  Photoperiodic responses of diapause termination, the effect of diapause-inducing, or diapause-terminating, photoperiod and temperature on diapause termination, and the time course of diapause in overwintering O. furnacalis larvae under natural conditions, were investigated by transferring larvae in which diapause had been induced under different conditions to different diapause terminating conditions. [Results]  Photoperiodic response curves for diapause termination showed that diapause termination was photoperiodically controlled with a critical day length of about 14.5 h. A rearing photoperiod of 13L︰11D evoked weaker intensity of diapause than did 11L︰13D and 12L︰12D at 25 and 28 ℃. When diapausing larvae were placed under 12L︰12D at 25 ℃ to 15L︰9D at 22, 25 and 28 ℃, the duration of diapause was significantly shortened with increasing temperature from 72 days at 22 ℃ to 34 days at 28 ℃. Chilling at 5 ℃ did not shorten the duration of diapause but synchronized pupation within the population. Transferring naturally overwintering larvae at different times to a short photoperiod of 12L︰12D, or a long photoperiod of 15L︰9D, at 25 ℃, indicated that larvae showed significant photoperiodic sensitivity during the early phase of diapause but that this declined until no photoperiodic sensitivity was detected after January. Field observations over 3 years revealed that 50% of pupae and adults of overwintering larvae occurred between the end of April and early and mid-May, respectively. [Conclusion]  Diapause intensity of the Asian corn borer can be significantly affected by both diapause- inducing, and diapause-terminating, photoperiods and temperatures.