Transiting exoplanets cross their host star disk, therefore high-precision transit light curve can provide a unique tool to probe the stellar surface in detail. We started a project using high-precision Kepler observation to detect variation in the number and distribution of features on the stellar surface as a function of time (during the Kepler's four-year operation), and thus we would be able to estimate the magnetic cycle for a sample of stars. Our first results surprised us, as we figured out that photometrically quiet stars are not quiet at all. Secondly, we detected magnetic cycle for several stars, although later we figured out that the periodicity which we detected arises from a very subtle and tiny noise in the Kepler observation.