Ochratoxin A (OTA) is a powerful mycotoxin that can cause severe damage to human health, and its detection has attracted considerable attention in the field of food science. We present a robust and facile label-free colorimetric aptasensor for OTA detection using the aptamer-enhanced oxidase-like activity of MnO2 nanoflowers. The catalytic activities of the nanozymes could be improved by adsorption of the aptamers onto the MnO2 nanoflowers due to the increased affinity of the nanoflowers for the chromogenic substrate. The linear range for OTA detection varied from 0.05 to 33.35 ng/mL with a detection limit of 0.069 ng/mL. The limit of detection of the proposed strategy is equivalent to or even better than those of several previous methods. Moreover, the colorimetric aptasensor exhibited good specificity and stability for the analysis of OTA in wheat flour and red wine samples. Therefore, this method appears to have promising applications in the detection of mycotoxins.