This study aimed to evaluate the forage production, nutritional value, soil chemical properties, and rhizosphere microorganism composition of maize–legume intercropping systems in fallow paddy fields. Before seeding, the fields were sprayed with 1000 kg ha⁻¹ of nitrogen composite fertilizer (NPK: 21-17-17). From 2020 to 2021, maize was intercropped with seven different legume cultivars at the National Institute of Animal Science, Cheonan, Republic of Korea. Of the seven legumes, the intercropped lablab (Lablab purpureus [L.] Sweet) and cowpea (Vigna unguiculata L. Walp) showed the greatest plant heights because the maize plants supported their climbing habit. The forage productivity of the intercropped soybean cultivars, Chookdu 1 and 2, lablab, and cowpea, was relatively high compared with those of the other legumes. Chookdu 1 and 2 showed higher forage productivity in monoculture than when intercropped. When intercropped with maize, the Daewon and Daepung soybean cultivars showed the lowest neutral detergent fiber and acid detergent fiber contents and the highest crude protein in 2020. However, the forage productivity of Daewon and Daepung was low, indicating unsuitability for intercropping with maize in paddy fields. The microorganism composition in the root rhizosphere showed a higher proportion of Proteobacteria under legume than maize cultivation. Proteobacteria were substantially more abundant in soils intercropped with lablab than in the lablab monoculture. Maize and cowpea appeared to be the best intercropping combination considering forage productivity and feed value. However, the Chookdu 1 and 2 cultivars and lablab also showed potential for intercropping with maize in paddy fields.