  We report the results of spectropolarimetric study of the classical Cepheid
$\eta$ Aql. We found that the longitudinal magnetic field of $\eta$ Aql
sinusoidally varies with the radial pulsation period, while the amplitude $B$,
mean field $B_0$, and phases of maximum and minimum field change from year to
year. We hypothesize that possible reasons of those variations are stellar
axial rotation or dynamo mechanisms.
