The Cr doping effects on the properties of La0.5Ca0.5MnxCr1-xO3 (0.02 <= x <= 0.08) films prepared by a pulsed laser deposition method have been studied by the photoinduced method. Upon Cr doping, the metal-insulator transition shifts to the lower temperature and the photoinduced relaxation time decreases at T=80 K. It is found that the maximum values of the photoinduced relative change in the resistance increase to reach the peak of about 37.11% at x=0.04 and then decrease with increasing the Cr doping content. These results show that the Cr doping effects on the properties of manganites is highly related to the Cr doping content. The introduction of a small amount of Cr cations induces an appearance of the ferromagnetic phases and the antiferromagnetic phases gradually become dominant with a further increase of the Cr ions. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.