Polyoxometalates (POMs) show great molecular diversity and have significant applications in material science as well as in medicine. In this study, nano-complexation of a novel europium containing polyanion [Cs⊂Eu6As6W63O218(H2O)14(OH)4]25− (EuWAs) with biocompatible chitosan was achieved through ionotropic gelation technique without the aid of any cross-linker. Thus obtained chitosan/EuWAs nano-complex was characterized using DLS and Zeta analysis, FT-IR, SEM, AFM, TG/DTA, EDAX and fluorescence spectroscopy. The cross-linking efficiency of EuWAs with chitosan was calculated to be 81% and the release profile recorded at physiological pH was slow and sustained. Cytotoxicity assays performed on a host of cancer cell lines, viz., KB, MCF-7, PC-3 and A549 proved the anticancer activity of the nanocomplex and flow cytometry studies revealed that reactive oxygen species generation can be the plausible mechanism for the apoptosis induced by this material. Our study has thus indicated the feasibility of using chitosan/EuWAs nano-complex for anticancer applications.