The effect of the coexistence of titanate nanosheets (TNS) with nanometric lateral dimensions (ca. 3 nm), which were prepared through a hydrolysis reaction of titanium tetraisopropoxide, on the catalytic activity of horseradish peroxidase (HRP) was investigated as a function of solution pH. Especially in diluted HRP solutions with a pH range of 7–8, enzymatic reaction rate, i.e. maximum velocity (V_max), in the conventional Michaelis–Menten equation, was significantly enhanced more than 2 times in the presence of TNS. In contrast, the increase in V_max was not very large in acidic (pH = 4.0) and basic solutions (pH = 9.0). It was demonstrated that the TNS brought about peptization of aggregates composed of several HRP molecules in a diluted solution, causing an increase in the apparent HRP concentration participating in the enzymatic reaction. Moreover, the TNS activated superoxide dismutase (SOD) with O₂⁻ scavenging performance.