Abstract: Because the intraseasonal oscillation (ISO) was found as a strong signal for the summer precipitation in the East Asia as shown in the recent studies, its climatic characteristics in the boreal subtropics and especially in the subtropical northern Pacific were revealed in this paper using the spatiotemporal spectrum method and wavelet analysis based on the NCEPNCAR Reanalysis Data for the period of 1958—2002. The specific results show as follows. The variance ratio of the ISO to all waves for the meridional wind over the subtropics is strikingly bigger than that in tropics, which is distinct from those for the zonal wind and height. At 850 hPa level, the waves with zonal wave numbers 4—6 and periods of 30—60 d or 70—90 d are dominant with the meridional wind for the intraseasonal scale (10—90 d) in despite of the dominant waves with zonal wave number 1 and periods of 30—60 d with the height and zonal wind. The power spectra of the westward propagation are all stronger than those of the eastward propagation for the above three variables. And it is found that an interseasonal “seesaw” of meridional wind ISO swings between the two regions, that is, the region from East Asia to the northwestern Pacific and the region of the northeastern Pacific, in which the power spectra of 30—60 d oscillations are the strongest in summer and weakest in winter in the former region and the reverse in the latter region, with the boreal spring and autumn just as the transition phases for the ISO activities for both the regions. In addition, the decadal and interannual variation characteristics of ISO over the subtropical North Pacific are presented in this paper which show that the ISO activities over the subtropical northwestern Pacific are moderate during 1958—1975, weak during 1976—1990, and robust during 1991—2000. During ENSO events occurring, the subtropical ISO presents quite different behaviors from those in the tropics and appears irregularly. However, the results of 2—7 year bandpass filter reveal that the ISO over the northwestern Pacific holds notable ENSO signals, while the 9 year lowpass filtered results manifest that the ISO variation over the northwestern Pacific are negatively correlated with the ENSO cycle and positively correlated over the northeastern Pacific.