Expression of cyclin D1 is required for cancer cell survival and proliferation. This is presumably due to the role of cyclin D1 in RB inactivation. Here we investigated the prosurvival function of cyclin D1 in a number of cancer cell lines. We found that cyclin D1 depletion facilitated cellular senescence in several cancer cell lines tested. Senescence triggered by cyclin D1 depletion was more extensive than that caused by the prolonged CDK4 inhibition. Intriguingly, the senescence caused by cyclin D1 depletion was independent of RB status of the cancer cell. We identified a buildup of intracellular reactive oxygen species, in the cancer cells that underwent senescence upon cyclin D1 depletion, but not in CDK4 inhibition, and that ROS buildup was responsible for the senescence. Lastly, the senescence was found to be instigated by the p38/JNK-FOXO3a-p27 pathway. Therefore, expression of cyclin D1 prevents cancer cells from undergoing senescence, at least partially, by keeping the level of intracellular oxidative stress at a tolerable sub-lethal level. Depletion of cyclin D1 promotes the RB-independent pro-senescence pathway, and cancer cell succumbing to the endogenous oxidative stress.