There is a need to understand the long-term variability Asian-Pacific Oscillation (APO) due to its close linkages with large-scale ocean–atmosphere anomalies. The first principal component (PC) of a network of 130 temperature proxies covering East Asia and the northeastern Pacific Ocean was employed to reconstruct the instrumental APO index from 500 to 2006. It explains 46.7% of the instrumental APO variance and correlates significantly with middle to upper tropospheric temperatures. The reconstructed APO reaches its peak in the Little Ice Age (LIA) and is low during the Medieval Climate Anomalies (MCA) period and since the 1850. The APO variations are caused by the temperature difference between East Asia and north Central Pacific Ocean. The Pacific Decadal Oscillations (PDOs) and tropical ocean-atmospheric features [the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD)] are reversely connected to APO variations particularly on long timescale (e.g. centennial timescale) and short timescale (e.g. interannual), respectively, possibly via modulating the strength of the Asian summer monsoon. However, the relationship between the APO and both external forcings (e.g. solar irradiation) and the PDO are quite variable, which is significant only when the influences of the coupled ocean-atmosphere patterns are weakened. The APO is positively correlated with indices of the hydroclimate of Monsoonal Asia, and is negatively associated with climatic indices for western North America.