In order to evaluate the effects of ethephon and nitrogen fertilizer on sweet sorghum cv. Sofra, an experiment was conducted as split plot on a randomized complete block design with three replications at Agricultural Research Station of Isfahan University (Isfahan, Iran). Experiment was conducted with four nitrogen levels (0, 100, 200 and 300 Kg urea ha^-1 from Urea with 0, 46, 92 and 138 Kg nitrogen ha^-1, respectively), as main plot and four ethephon concentrations (0, 800­, 1000 and 1200 ppm) as sub-plots. Preparing land, fertilizing and weed control with Tereflan herbiside at 1.5 L/ha performed pre-sowing was conducted before planting. Every plot was 3×4 meter with 6 rows. The final populations of plants were 200,000 plants/ha and used seeds were 10 Kg/ha. Ethephon was sprayed on shoot at booting stage. Irrigation was performed every 10-12 days with flooding irrigation method. Plants were harvested at physiological maturity stage. Biological yield as well as stem yield was increased by increasing ethephon and nitrogen fertilizer. The highest biological yield (32.53 t ha^-1) was obtained at 1200 ppm of ethephon and 300 Kg ha^-1 of urea application. The maximum amount of stem yield (30.91 t ha^-1) was obtained by application of the highest levels of nitrogen and ethephon (300 Kg urea ha^-1 and 1200 ppm Ethephon). The highest harvest index (35.20%) was obtained at control (no ethephon application) and the lowest (9.70%) with the application of 1200 ppm of ethephon. The highest hundred grain weight (1.91 g) was obtained with the application of 800 ppm of ethephon.