New BV light curves of the short-period eclipsing binary system DD Mon have been obtained. Light-curve variability is seen in both B and V bands as compared with the light curves obtained in 1986 by Yamasaki et al. (1990AJ.....99.1218Y). The light curves are analyzed by using Wilson-Devinney's synthetic light-curve program, and the present photometric solution reveals that DD Mon is a near-contact binary with the secondary component filling the Roche lobe. Combined with Yamasaki et al.'s (1990AJ.....99.1218Y) spectroscopic results, absolute quantities of DD Mon are derived: mass of the primary M_1_=1.05+/-0.08M_{sun}_, mass of the secondary M_2_=0.47+/-0.04M_{sun}_, radius of the primary R_1_=1.36+/-0.04R_{sun}_, radius of the secondary R_2_=1.03+/-0.03R_{sun}_. These results show that the components of DD Mon have evolved away from the ZAMS and through a mass-transfer process to the present semi-detached state. The variation in shape of the light curve may be caused by the evolution of the system and the activity of dark spots.