  We report the observations of X-ray oscillations during the flare in a cool
active star XI Boo for the first time. XI Boo was observed by EPIC/MOS of the
XMM-Newton satellite. The X-ray light curve is investigated with wavelet and
periodogram analyses. Both analyses clearly show oscillations of the period of
1019 s. We interpret these oscillations as a fundamental fast-kink mode of
magnetoacoustic waves.
