This study uses mooring data from two years (November 2017 to October 2019) to estimate downward energy flux (Fz) of near-inertial waves (NIWs) in the Kuroshio Extension. By dividing the data into 11-day segments, the temporal variability of the effective near-inertial frequency and group velocity due to background mesoscale motions (BMMs) was considered. During winter when NIWs were active, on average in anticyclonic circulations, Fz increased by 50%, while in cyclonic circulations, Fz decreased by 45% when the BMMs were considered. Since cyclonic circulations are twice as frequent, Fz decreased by approximately 17%, or 0.37 x 10-3 W m-2. This amount is approximately 1.8 times greater than that in the northeastern Pacific and accounts for approximately 28% of the wind work rate, similar to high-resolution numerical model results. Thus, the Kuroshio Extension is an important area for NIWs energy transfer, and BMMs should be considered for accurate NIWs energetics.