Using observed rainfall data from 26 stations in Southwest China for the period 1951–2017, in this study, we investigated the climatic characteristics of rainfall over Southwest China during spring (March–April–May) and each spring month. The rainfall in May was found to account for 55.3% of the total spring rainfall over Southwest China and to have the most significant interannual variations of the spring months. The spring rainfall over Southwest China also shows clear interdecadal variations, which are dominated by the interdecadal variations of the May rainfall. Significant abrupt interdecadal changes (AIDCs) also occur in the spring rainfall, with increased AIDCs having occurred in the middle and the later 1990s after a period of decreased IDACs in the later 1970s. Although the time series of spring rainfall over Southwest China exhibits an insignificant linear trend, the eastern part of Southwest China shows a clear decreasing trend in terms of area, and the western part of Southwest China shows a significant increasing trend. Lastly, the spring rainfall over Southwest China shows significant interannual and interdecadal periodicities, which are also present in the April and May rainfalls. We note that no interdecadal periodicity is evident for March rainfall. In general, the interannual and interdecadal periodicities of spring rainfall are dominated by the variations of May rainfall.