The authors investigated the interbasin interactions between the Pacific and Atlantic Oceans depending on the phase relationship of Pacific decadal oscillation (PDO)/Atlantic multidecadal oscillation (AMO) based on observations and idealized model experiments. When the AMO and the PDO are in phase (i.e., +PDO/+AMO or −PDO/−AMO), the Pacific Ocean regulates the SST anomalies in the equatorial Atlantic Ocean with altering of the Walker circulation. During this period, there is a negative SST–precipitation relationship in the equatorial Atlantic Ocean where the atmosphere forces the ocean. In contrast, when they are out of phase (i.e., either +PDO/−AMO or −PDO/+AMO), the Atlantic Ocean influences the equatorial Pacific Ocean by modifying the Walker circulation, resulting in a westward shift of a center of convective forcing in the equatorial Pacific Ocean compared to that during an in-phase relationship of PDO/AMO. During this period, a positive SST–precipitation relationship is dominant in the equatorial Atlantic Ocean where the ocean forces the atmosphere. To verify this result, we conducted pacemaker experiments using the Nanjing University of Information Science and Technology Earth System Model version 3 (NESM3). Model results supported our findings obtained from the observations. We infer that the characteristics of the Pacific–Atlantic interbasin interactions depend on whether the PDO and AMO phases are either in phase or out of phase.