The climatic changes and the irregularity of the seasons of rain involved the adoption by the farmers of the varieties more plastic and adapted in their zone of culture that the improved varieties. In the objective to measure the response of the ecotypes to photoperiodism, a study of the sensitivity of 120 ecotypes of sorghum of Burkina Faso to the photoperiod was made using a test comprising two dates of sowing. These ecotypes come from the germplasm of the University of Ouagadougou, made up between 1984 and 1986 within the framework of the safeguarding of the diversity of the sorghum. It comes out from this study that all the studied ecotypes are photoperiodic and systematically reduce their cycle at the time of a delay the semi one. Also let us note that 46 % of the ecotypes showed a sensitivity moderate to the photoperiod (0<K?0,3), 38% a relatively significant sensitivity (0,3<K?0,6) and 16 % a strong sensitivity (0,6 < K?0,9). The flowering of the ecotypes occurred in the 25 days which preceded the average date by end of the rain season and floral initiation started and finished during the time to which the day is shorter than the night. We retain as this study as at the time of a delay of 3 weeks sowing the ecotypes lose 10 to 96% their seeds with an average of 66%.