Previous studies have demonstrated significant increases in atmospheric rivers (ARs) over the western North Pacific (WNP) during post–El Niño summers, which primarily focus on seasonal-mean features of ARs. Here, we aim to compare the AR characteristics during AR-active weeks in post–El Niño and non-post–El Niño summers, and to clarify their distinct mechanisms. Our results reveal that the patterns of WNP ARs and associated atmospheric and oceanic variabilities vary significantly between the two cases. During AR-active weeks in post–El Niño summers, a meridional dipole of anomalous geopotential height dominates the WNP with a more westward-located WNP subtropical high, resulting in enhanced AR activity extending from southern China into the central Pacific. In contrast, during AR-active weeks in non-post–El Niño summers, a prominent zonal dipole appears featured by an anomalous low pressure over southeast China and an anomalous high pressure over subtropical WNP, together with pronounced sea surface temperature (SST) warming to the southeast of Japan due to the more downward shortwave radiation. Such anomalous circulation leads to more AR occurrence spreading from the northern South China Sea (SCS) to Japan. The fraction of rainfall associated with ARs indicates distinct regionality reflecting the above AR features, especially over eastern China and Japan. The temporal decomposition reveals the basic state plays a more dominant role in the anomalous circulation during AR-active weeks in post–El Niño summers than in non-post–El Niño summers. Furthermore. the possible impacts of TC in the two cases are also suggested.