Abstract: Using the polar vortex oscillation (PVO) index established in an isentropic Po tentialVorticity coordinate and based on the NCEP/NCAR reanalysis data and the weekly NOAA -OISST-V2 SST data, the temporal and spatial connections of the stratospheric PVO to the ENSO tropical SST over monthly timescale are investigated through the correlation, regression and composite analyses. It is found that the significant connections exist mainly at the inter annual timescale of about 3-5 year, representing the relationships between the inter annual PVO trend and the ENSO SST anomalies. Firstly, the temporal connections between the two phenomena are not contemporary as expected, but rather that the maximum negative correlation occurs when the ENSO tropical SST anomalies lead the PVO for 9-11 months. Warmer (colder) ENSO SST anomalies tend to be followed by a negative (positive) inter annual trend of PVO, or a weaker (stronger) polar vortex. The composite and statistical results further verify that there tend to be more and stronger negative PVO events followed in the case of a warmer ENSO SST event occurred in the previous period, and vice versa. The warmer ENSO SST may also favor a higher frequency of PVO events than colder SST regardless of positive or negative PVO events. Further, it is found that, following the significant responses in the tropical troposphere and stratosphere to the warmer ENSO SST, there exist a seies of simultaneous poleward and downward propagations of temperature anomalies from the tropics to the polar region, which are coincidently related with the PVO anomalies 9-11 months later. This may suggest that, as in the intraseasonal variations of the PVO, the inter annual variation of PVO associated with leading ENSO SST anomalies might also be accompanied with the interannual variations of the global mass circulation. This linkage of the tropical SST to the extra tropical PVO trend implies basically new opportunities for the extended climate prediction.