The magnetic structure of a magnetic dot depends on its geometrical factors such as thickness and dot size and can be either a multidomain state or a vortex state. The magnetoresistance (MR) of a series of magnetic dots with diameters ranging from 0.3 to 5 μm was measured to investigate the correlation between domain-structure and magnetotransport properties. A dot with a diameter of less than 2 μm has a domain of vortex state at remanence and demonstrates similar reversible MR results. Moreover, the behaviors of MR show clear changes corresponding to the domain-structure change from vortex to multidomain states with an increasing dot diameter. Data can be qualitatively described by the anisotropic magnetoresistive effect. Hence, our results show that the magnetotransport can be a tool to detect the magnetic domain structure of a submicron magnetic dot.