Multiple enzyme-like activities of manganese oxides (MnO 2 ) have been reported and applied in catalysis, biosensors, and cancer therapy. Here, we report that catechol can be determined colorimetrically based on the 3,3',5,5'-tetramethylbenzidine (TMB) oxidase-like activity of δ-MnO 2 . The detection was based on pre-incubation of catechol containing water samples with δ-MnO 2 , and then the residual TMB oxidase-like activity of reacted δ-MnO 2 was linearly dependent on the catechol concentration in the range of 0.5 to 10 μM. This determination method was stable at pH 3.73-6.00 and was not affected by ion strength up to 200 μM. Common co-solutes in water bodies (50 μM) have negligible effects and excellent selectivity of catechol among various phenolic compounds (15 μM) was facilitated. Both reduction and aggregation of δ-MnO 2 were observed during the incubation process with catechol, and aggregation-induced TMB oxidase-mimic activity decrease was the main factor for this colorimetric determination.