The present study was conducted to clarify the effect of temperature and daylength on heading in diploid rhodesgrass cultivars. Three diploid cultivars, Tochiraku-kei, Fords-Katambora and Pioneer, were planted 9 times at 10-day intervals between April 24 (I) and July 14 (IX) in 1975. In 1976 the 3 cultivars were planted 3 times at 1-month intervals on May 4 (II), June 4 (V) and July 4 (VIII) under 5 daylength treatments of natural daylength (ND), 12 h daylength (12 h), 24 h daylength (24 h), 24 h/ND,and 24 h/12 h. DH (days to heading) decreased linearly with the increase in DMT (daily mean temperature) commonly in the 3 cultivars in 1975, suggesting that temperature is a major factor determining DH in diploid rhodesgrass. This relationship is described by a linear regression equation between DH and DMT in the period from sowing to heading date. From the results in 1976, a short daylength is considered to have an effect for accelerating flower initiation of diploid rhodesgrass under temperatures more than 22℃. These research findings would be useful in diploid rhodesgrass for estimating the first cutting time and/or seed harvesting time, and for conducting effective reproduction in greenhouses during winter.