GU Ori was observed with the 1 m telescope at Yunnan Observatories in 2005. To determine its physical properties, the Wilson-Devinney program was used. The results reveal that GU Ori is a W-subtype shallow contact binary with a more massive but cooler second star. The masses of its two component stars are estimated to be M-1 = 0.45 M-circle dot, M-2 = 1.05 M-circle dot. The O'Connell effect was reported to be negative on the light curves observed in 2005. However, it changed to a positive one on the light curves observed from 2011 to 2012. The mean surface temperatures of star 2 (T-2) determined by the two sets of light curves were different, which may result from stellar activity. The O - C diagram shows that the period of GU Ori is decreasing at a rate of dP/dt = -6.24 x 10(-8) dyr(-1), which may be caused by mass transfer from star 2 to star 1 with a rate of dM(2)/dt = -2.98 x 10(-8) M-circle dot yr(-1). GUOri is a contact binary with quite high metallicity.