Tubular micromotors composed of a hybrid single-wall carbon nanotube (SW)-Fe2O3 outer layer and powered by a MnO2 catalyst are used for phenylenediamines isomers detection and discrimination. Catalytic decomposition of H2O2 as fuel results in the production of oxygen bubbles and hydroxyl radicals for phenylenediamines dimerization to produce colorful solutions in colorimetric assays. The combination of Fe2O3 nanoparticles along with the irregular SW backbone results in a rough catalytic layer for enhanced hydroxyl radical production rate and improved analytical sensitivity. Such self-propelled micromotors act as peroxidase-like mobile platforms that offer efficient phenylenediamines detection and discrimination in just 15 min. Factors influencing the colorimetric assay protocol, such as the navigation time and number of motors, have been investigated. Low limits of detection (5 and 6 μM) and quantification (17 and 20 μM) were obtained for o-phenylenediamine and p-phenylenediamine, respectively. The magnetic properties of the outer SW-Fe2O3 hybrid layer allow the reusability of the micromotors in the colorimetric assay. Such attractive performance holds considerable promise for its application in sensing systems in a myriad of environmental, industrial, and health applications.