We analyzed the effects of plowing on root systems and root lodging of maize (Zea mays L.) in comparison with rotary tilling in upland fields converted from paddy fields in Gleysol. The percentage of soil water potential more than -3.1 kPa before the 6th leaf stage tended to be smaller following plowing than rotary tilling; and drainage was improved with plowing. Soil temperature at depths of 5 and 10 cm during the growing season was similar between the tillage treatments. Dry weight and leaf area index did not differ much between tillage treatments. Root length density and root weight density did not differ much between the tillage treatments, but root length and the percentage of root length at a depth of 0-5 cm tended to be higher with plowing than with rotary tilling, and the root depth index, which indicates the mean root depth, tended to be smaller with plowing than with rotary tilling. Although traits of root lodging (culm length, ear height, horizontal pulling resistance (HPR), and HPR-value) did not differ much between the tillage treatments, and root lodging status was lower with plowing than with rotary tilling. These results indicate that the root systems of maize in upland fields converted from paddy fields in Gleysol were shallower with plowing than with rotary tilling, and root lodging was alleviated by plowing. Plowing is expected to reduce lodging effects in maize grown in upland fields converted from paddy fields.