To determine the most suitable sowing date for obtaining the maximum forage and grain yield of promising lines of Foxtail Millet this research was carried out as split-plot arrangement in randomized complete block design with three replications in 2008 and 2009 growing seasons in Birjand research field station, Birjand, Iran. Sowing dates, 22 May, 05 June, 22 June and 06 July were assigned to main plots and five Foxtail Millet promising lines were randomized in sub-plots. Tiller number plant-1, leaf number plant-1, plant height, panicle length, stem diameter, grain number panicle-1, 1000 grain weight, grain yield and forage yield were measured and recorded. Results indicated that grain yield was greater in second and third sowing dates with 4.3 and 4.6 tons ha-1, respectively. Fresh forage yield in the first sowing date with 25.6 tons ha-1 was the highest among the sowing dates. Dry forage yield was also greater in the fourth and first sowing dates as compared with the second and third sowing dates. KFM5 promising line with 4.9 tons ha-1 grain yield and 24.7 tons ha-1 fresh forage yield performed superior in comparison with other promising lines. The highest dry forage yield was obtained from KFM15 in the first sowing dates.