This study documents the decadal changes of the spring meridional circulation (SMC) over 110°E–165°E and the relationship between the SMC and summer (June-July-August-September) typhoon activity over the Western North Pacific (WNP) during 1948–2010. The authors found that the SMC was changed after 1969. Be-fore its change, the SMC had no clear relation with the summer typhoon number over the WNP (TNWNP), but after the change, it has become positively correlated with the TNWNP, with a correlation coefficient of 0.57 be-tween them (above the 99% confidence level). It was ob-served that after the SMC was changed, the positive tropical sea surface temperature anomaly associated with the SMC was shifted from the Equatorial Eastern Pacific (El Ni?o) to the equatorial middle Pacific (El Ni?o Mo-doki); at the same time, the Pacific decadal oscillation (PDO) pattern over the North Pacific, which is associated with the SMC, was enhanced. The SMC and the TNWNP are both modulated by the El Ni?o Modoki after 1969, so the relationship between them becomes significant.