Abstract: The effects of photoperiod and temperature on diapause inducing of the greatmormon butterfly Papilio memnon were studied, which came from the population of Emei areas, Sichuan Province. The effects of photoperiod on diapause were related to temperature. Under constant temperature 20 ℃, the percentage of diapause individualswent upwith the shortening of daylength during 12 h to 13 h, and reached to 100% when daylength less than 12. 5 h. Underconstant temperature 25 ℃, the percentage of diapause individualswent up with the shortening of daylength during 11h to 13. 5 h, too, and arrived 94. 5% when daylength at 12 h, but the percentage didnot arrive to 100%. Under con2stant temperature 30 ℃, no diapause happened. The effects of temperature on diapause were also related to photoperiod. Under the same daylength and in the range of test temperature, the percentage of diapause individualswent downwith temperature increasing. When temperature arrived to 30 ℃, no individual went to diapause whether daylengthshort or long. Only short daylength and low temperature were benefit to diapause, long daylength and high temperaturewere benefit to growth. Short daylength had a cumulative effect for inducing diapause. Under constant temperature 20 ℃, the critical photoperiod of Papilio m em non was LD 13 h 11 min∶10 h 49 min, under constant temperature 25℃, the critical photoperiod wasLD 12 h 49 min∶11 h 11 min. The critical daylength shortened with the rising of temperature. The fifth instar larvae of Papilio m em non is the sensitive stage to photoperiod.