Purpose. To investigate the effect of partial ablation of melanopsin-containing retinal ganglion cells (mcRGCs) on nonimage-forming (NIF) visual functions in rd mice lacking rods. Methods. The rd mice were intravitreally injected with different doses (100 ng/mu l, 200 ng/mu l, and 400 ng/mu l) of immunotoxin melanopsin-SAP. And then, the density of ipRGCs was examined. After establishing the animal models with different degrees of ipRGC damage, a wheel-running system was used to evaluate their reentrainment response. Results. Intravitreal injection of melanopsin-SAP led to partial ablation of ipRGCs in a dose-dependent manner. The survival rates of ipRGCs in the 100 ng/mu l, 200 ng/mu l, and 400 ng/mu l groups were 74.14% +/- 4.15%, 39.25% +/- 2.29%, and 38.38% +/- 3.74%, respectively. The wheel-running experiments showed that more severe ipRGC loss was associated with a longer time needed for reentrainment. When the light/dark cycle was delayed by 8 h, the rd mice in the PBS control group took 4.67 +/- 0.79 days to complete the synchronization with the shifted cycle, while those in the 100 ng/mu l and 200 ng/mu l groups required 7.90 +/- 0.55 days and 11.00 +/- 0.79 days to complete the synchronization with the new light/dark cycle, respectively. Conclusion. Our study indicates that the regulation of some NIF visual functions is dependent on a certain minimal number of intact functional ipRGCs.