Lanthanides have been reported to induce apoptosis in cancer cell lines. Human cervical cancer cell line HeLa was found to be more sensitive to dicitratolanthanum (III) complex ([LaCit2](3-)) than other cancer cell lines. However, the effect and mechanism of dicitratoytterbium (III) complex ([YbCit2](3-)) on HeLa cells is unknown. Using biochemical and comparative proteomic analyses, [YbCit2](3-) was found to inhibit HeLa cell growth and induce apoptosis. Similar to the effects of [LaCit2](3-), proteomics results from [YbCit2](3-)-treated cells revealed profound changes in proteins relating to mitochondria and oxidative stress, suggesting that mitochondrial dysfunction plays a key role in [YbCit2](3-)-induced apoptosis. This was confirmed by the decreased mitochondrial transmembrane potential and the increased generation of reactive oxygen species in [YbCit2](3-)-treated cells. Western blot analysis showed that [YbCit2](3-)-induced apoptosis was accompanied by the activation of caspase-9 and specific proteolytic cleavage of PARP, leading to an increase in the pro-apoptotic protein Bax and a decrease in the anti-apoptotic protein Bcl-2. These results suggest a mitochondrial pathway of cell apoptosis in [YbCit2](3-)-treated cells, which will help us understand the molecular mechanisms of lanthanide-induced apoptosis in tumor cells.