In the eastern Great Plains, grain sorghum [Sorghum bicolor (L.) Moench] and soybean [Glycine max (L.) Merr.] are commonly grown in rotation, but cropping-sequence effects for these two crops have not been thoroughly evaluated in this region. A 10-year field study was conducted in southeastern Kansas to evaluate the effects of various grain sorghum and soybean cropping sequences on grain yield of both crops and to determine the influence of two fertilizer nitrogen (N) rates (84 and 150 kg N per hectare) on grain yield and N concentration of plant and grain for rotated and non-rotated grain sorghum. Cropping sequences were: (i) 1st, 2nd, 3rd, 4th, and 5th year of each crop after 5 years of the other crop, (ii) an annual rotation of each crop, and (iii) continuous monoculture of each crop. Grain yields of both soybean and grain sorghum were highest for the 1st-year crop after five years of the other crop, averaging 33 and 15% more than yield of the respective monoculture crop. Grain yields of both crops declined with increasing years of consecutive planting. Grain yields of rotated sorghum (1st year and annually) were maximized with 84 kg N per hectare, whereas other cropping sequences required a higher N rate to optimize grain yield. Plant and grain N concentrations also were higher for rotated grain sorghum than for monoculture. The results from this long-term study clearly demonstrate the beneficial effect of crop rotation on soybean and grain sorghum yields and also re-affirms that the fertilizer N requirement for grain sorghum is reduced significantly when it is rotated with soybean.