The study was carried out with the aim to determine optimum sowing date and growing degree-days (GDD) of sweet corn using different sowing dates from April to June during the 2009 and 2010 growing seasons under semi-arid ecological conditions of the Southwestern Anatolia Region. The research included five sowing dates 1st April, 15th April, 1st May, 15th May and 1st June. The experiment was set up as Randomized Complete Block Design with three replications. Lumina F-1 hybrid sweet corn cultivar was used as an experimental materials. Sowing dates had a significant effect on harvest period, emergence rate, fresh ear yield and yield characteristics. Compared with the corn, sowing dates from April to June the corn sowed in the earlier had longer total growth period. The maximum fresh ear yields (14648.3 and 14568.3 kg ha(-1), respectively) were obtained from May 1 and the highest fresh ear number (64976.7 and 64915.7 number ha(-1), respectively) recorded from May 15 sowing date in 2009 and 2010 years. The highest emergence rate (93.3 and 91.7 %, respectively) was determined from June 1 in both years. The highest ear diameter (44.8 and 44.9 mm), ear length (18.7 and 18.3 cm, respectively), number of kernels per ear (566.4 and 551.7 grain, respectively) and ear weight (225.2 and 224.7 g, respectively) were observed from May 1 sowing date in 2009 and 2010 years. Total GDD accumulated as milk stage period of sweet corn in different sowing dates occurred between 578.9-938.8 C-0 in 2009 and 646.7-1025.5 C-0 in 2010.