The most significant climatological intraseasonal oscillation (ISO) periods of summer rainfall over the middle and lower reaches of the Yangtze River (M-LYR) are investigated by using the gauge-based daily precipitation analysis data of China and the NCAR/NCEP reanalysis data from 1979 to 2013. It is found that the oscillation periods of summer rainfall at the intraseasonal timescale show remarkable difference between the MYR and LYR. The 10-30-day oscillation is the primary mode over the MYR, while the longer period of 30-60-day dominates the LYR. The phase composite analysis is applied to reveal evolutions of intraseasonal circulation and vertical structure associated with these two periods of climatological ISO precipitation over the Yangtze River. In the upper troposphere at 200 hPa, it shows that a wave train over the mid-high latitudes propagates eastward, affecting the summer rainfall over MYR, while the southwestward propagation of the weakened Okhotsk blocking high is associated with the 30-60-day rainfall oscillation over LYR. The vertical structures of wind vorticity and divergence/convergence exhibit different features during their moving toward the Yangtze River. 10-30-day anomalous vorticity and divergence/convergence move southward toward the MYR; however, the 30-60-day anomalies move northward from the tropics. Atmospheric moisture from the South China Sea and from north of the Yangtze River converges over MYR, leading to favorable condition for the occurrence of rainfall. In contrast, the moisture in the LYR primarily comes from the tropics. Large amounts of atmospheric moisture originate from the eastern Indian Ocean, move through the Bay of Bengal and the South China Sea, converge with moisture transported westward from the western tropical Pacific, and then move northward, reaching the LYR. The results explain from the perspective of upper-level circulation and vertically integrated moisture flux why the 10-30-day oscillation mode of rainfall over MYR propagates southward, while the 30-60-day oscillation mode of rainfall over LYR propagates northward.