  The new B and V photoelectric observations of the beta Lyrae eclipsing binary
DO Cas were obtained on 6 nights form December 2000 to January 2001. The
observations were made at the Biruni Observatory, Shiraz, Iran and the light
curves are analyzed using the Wilson light curve synthesis and differential
correction code. So, the relative surface luminosities, new light elements, and
new orbital elements have been obtained, and from times of minimum the period
is improved. With these and previously published times, the period variation is
studied and a constant period is approved, though some authors has mentioned
some variations. The solutions of the light curves suggest that DO Cas is a
contact binary.
