Rice cropping areas have recently been restricted or reduced under the policy of the South Korean government. Therefore, the development of new crop or cropping systems is essential. Foxtail millet (Setaria italica.) is considered among the best candidate crops to substitute for rice, but there is limited information about maintaining or improving the grain yield without crop damage caused by excessive water content in sandy paddy fields. A two-year study from 2013 to 2014 was conducted in a trial field in the southern part of Korea (N 35°05′ 16.8″, E 127°56′ 34.6″). The three cultivars selected-Gyeongkwan 1, Samdachal, and Hwanggeumchal-are the most common varieties of foxtail millet in South Korea due to their highly functional nutrients and potential productivity. For the purpose of establishing the stable production of Foxtail millet in paddy-upland rotation fields, the effects of ridge width (60, 120 and 240 cm) on soil moisture in the ridge, and on the growth and yield of foxtail millet were investigated in a sandy paddy field. Soil water content increased in line with increasing ridge width. Therefore, the estimated retention time of excessive soil water during the cultivation period tended to increase in line with increasing ridge width. Foxtail millet plants reached the highest level of height in the 60-cm ridge width treatment in both years of the study. The grain yields in 2014 were 3.44, 3.77, and 3.28 tons・ha^-1 for Gyeongkwan 1, Samdachal, and Hwanggeumchal, respectively, grown in the 60-cm ridge width. The plant height and yield of foxtail millet had increased with a narrowed ridge width because soil-moisture conditions are remedied by ridge width. Therefore, we recommend that a ridge width of 60 cm be maintained to prevent excessive water damage to foxtail millet growth in a sandy paddy field.