In the past years, few grain sorghum varieties with limited yield potential have been developed and grown in Korea. Hybrids tend to be more productive and resistive to unfavorable environmental conditions than pure line varieties. However, no hybrid cultivars are available and never have been planted for grain sorghum in Korea. The main aims of this study were to (i) verify if US x Korean and US x US hybrids increase grain yield in Korea; (ii) assess the performance of waxy hybrids in Korea and the US; (iii) estimate general combining ability and specific combining ability for the lines studied; and (iv) identify superior lines and hybrids for future use in breeding. Two distinct sets of waxy-endosperm sorghum hybrids derived from Korean landraces and US lines (Texas A&M University) were tested in the US and Korea. Compared to the parental lines, hybrids derived from US lines and Korean landraces showed yield increase that ranged from 2% to 127%. Hybrids created from US lines showed higher heterosis than US x Korean hybrids. Hybrid vigor was observed in the US and Korea, but shifts in ranks of hybrid performance occurred. The results indicate that it is feasible to develop grain sorghum hybrids adapted to Korean conditions only if delibrate selections take place in Korea. A combination of Korean and US sources could provide an acceptable germplasm base for developing Korean landrace based sorghum hybrids.