Nano/Micro-scale magnetic sensors have been comprehensively investigated in recent decades. Among these sensors, anisotropic magnetoresistive (AMR) magnetic sensors have been well known for its simple and compact configuration. Recently, some researchers demonstrated that the magnetoresistance of a magnetic nanobar array can be changed by applying an external magnetic field orthogonal to the nanobar . However, the changing-ratio of the magnetoresistance is small when the applied magnetic field is low. To address this issue, many researchers demonstrated that the magnetoresistance changing-ratio can be significantly increased by changing the geometry of the magnetic structures (such as patterning the magnetic structures into disk- and oval- shapes to reduce the magnetic anisotropy to increase MR changing-ratio). In addition, some researchers recently studied that changing the dimension of the magnetic disk- and oval- structures (through size-effect) can significantly transform the magnetic domain into a stripe, vortex, or single domain, and changing the iteration can influence the magnetic-domain interaction in the magnetic disk- and oval- arrays . According to these results, we believe these concepts (changing the geometry, dimension, and iteration of the domain array) can be modified and combined to demonstrate a significant magnetoresistance change through the nanoscale magnetic-domain transformation among stripe, vortex, and single domains. Hence, in this article, we present a novel AMR magnetic sensor utilizing the nanoscale magnetic stripe/vortex/single domain transformation.