We present BVRI light curves with complete phase coverage for the short-period (p=0.377day) eclipsing binary star GR Boo. We carried out the observations using the SARA 90cm telescope located at Kitt Peak National Observatory. We obtained six new light curve minimum times. By fitting all of the available O-C minimum times, we obtained an updated ephemeris that shows the orbital period of GR Boo is decreasing at a rate of dP/dt=-2.36x10^-7^days/year. This decrease in its period can be explained by either mass transfer from the more massive component to the less massive one, or angular momentum exchange due to magnetic activities. We also obtained a set of revised orbital parameters using the Wilson & Devinney program. And finally, we concluded that GR Boo is a contact binary with a dark spot.