Clubroot caused by Plasmodiophora brassicae is a serious soilborne disease on cruciferous crops worldwide. Agricultural practice is a preferable clubroot management strategy due to its low investment requirement and environmental safety. Among the agricultural practices, solarization has been widely applied in the integrated management of other soilborne diseases. However, there are only a few reports on the effect of solarization on clubroot management. In this study, we measured the effect of plastic mulching on soil temperature at different depths and on clubroot incidence and severity under greenhouse and field conditions. The pathogen density in soil after solarization was measured by quantitative PCR analysis. Results indicated that the mulching treatment was able to increase soil temperature especially in the soil layer ranges of 0 to 20 cm. Solarization with mulching also effectively reduced the incidence and severity of clubroot in the greenhouse assay and the field trial by decreasing P. brassicae population in the soil. This study suggested that solarization with mulching can impair clubroot development and thus contribute to the sustainable management of clubroot.