Abstract: Seventy seven current cultivars,including early-crop and late-crop types,were subjected to 15 treatments of natural and artificial daytength ranging through 8.0,10.0,10.5,11.0,11.5,12.0,12.5,13.0,13.5,14.0,15.0,18.0,21.0,24.0 hours for 17 seasons within 8 years in 1980-1987.Data were treated statistically by means of the computer.Thus,according to their photoperiod qualities,the current rice cultivars could be divided into 4 types:insensitive type,weakly sensitive type,strongly sensitive type,extremely sensitive type;and considering day length and temperature together,could be divided into 4 types too.1.the dayltength sensitive and temperature weakly to moderately sensitive type,2.the day length weakly sensitive and temperature moderately sensitive type,3.the daylength strongly sensitive and temperature moderately sensitive type,4.the daylength extremely sensitive and temperature moderately to strongly sensitive type.In addition,regression equations of the representative type cultivars were established.The daylength extremely sensitive type had a strictly critical daylength.With increased leafage,the daylength strongly sensitive type became less stringent in its heading daylength.