  We present an analysis of NGC2204-S892 -- a new detached eclipsing binary
composed of two late K dwarfs. Based on three photometric campaigns launched in
2008 we obtained 5 light curves (3 in V, 1 in B and 1 in I), and derived an
orbital period of 0.451780+-0.000001 d. We also obtained 20 VLT/UVES spectra,
enabling accurate radial velocity measurements. The derived masses and radii of
the components (m1 = 0.733 +-0.005 Msun and R1 = 0.72 +-0.01 Rsun; m2 = 0.662
+-0.005 Msun and R2 = 0.68 \+-0.02 Rsun) are consistent with the empirical
mass-radius relationship established recently for lower main sequence stars in
binary systems; in particular we find that both stars are oversized compared to
theoretical models. NGC2204-S892 is very active: both components show variable
emission in Halpha and Hbeta and are heavily spotted, causing the light curve
to show appreciable changes on a timescale of weeks. Our results add to the
increasing evidence that the observed inflation of the radii of K and M stars
is related to high levels of magnetic activity.
