  We analyse oscillations observed in the X-ray light curve of the late-type
star AT Mic. The oscillations occurred during flare maximum. We interpret these
oscillations as density perturbations in the flare loop. Applying various
models derived for the Sun, the loop length and the magnetic field of the flare
can be estimated. We find a period of 740 s, and that the models give similar
results (within a factor of 2) for the loop length (~5.4e10 cm) and the
magnetic field (~100 G). For the first time, an oscillation of a stellar X-ray
flare has been observed and results thus obtained for otherwise unobservable
physical parameters.
