Heteropolyacids (HPAs) are a class of polyoxometallates (POMs) with oxygen-rich surfaces. Herein, we have developed an Fe-containing heteropolyacid by cation-exchange and employed KFePW12O40 nanostructures for Fenton, photo-Fenton and enzyme-mimetic reactions. The as-prepared KFePW12O40 catalyst exhibits efficient degradation of Rhodamine B (RhB) via the photo-Fenton reaction. As an enzyme-mimetic, this material can effectively oxidize TMB and dopamine. The obtained nanomaterials were characterized via SEM, TEM, XPS, BET surface area, TGA, UV-Vis spectroscopy, FT-IR, and XRD techniques. The photocatalyst has a relatively large surface area of 38 m2 g-1, and the Keggin structure of phosphotungstic ions is kept intact during the preparation. The RhB dye pollutants can be efficiently bleached and degraded up to about 80% within a one hour photo-Fenton reaction under visible light irradiation. Our results indicate that the KFePW12O40 nanomaterial can effectively mimic the enzyme cascade reaction of horseradish peroxidase (HRP). It also has a high affinity toward 3,3',5,5'-tetramethylbenzidine (TMB) for oxidation and henceforth, it has been used for the colorimetric assay of dopamine and H2O2. Overall, our study suggests that KFePW12O40 can be used for the efficient degradation of environmental pollutants. The KFePW12O40 catalyst is stable and can be easily separated from the reaction system for reuse without an obvious loss of activity.