Miniaturization of mechatronic devices has important uses and advantages. Nanostructures are relevant in this context. In this chapter, different nanostructures of polyaniline (PANI) and their preparation are briefly introduced. The novel Y-junction PANI nanorods and nanotubes are described in more detail. The morphology of Y-junction PANI nanostructures (rods and tubes with diameter in the range of 40–100 nm) is confirmed by transmission electron microscopy (TEM), and the effects of reaction conditions on the morphology of PANI nanostructures are investigated. Further characterization experiments including FTIR, UV-vis spectrometry, and x-ray diffraction are carried out to study the chemical and electronic structures of the PANI nanostructures. The magnetic property of the Y-junction PANI nanorods with Fe3O4 nanoparticles is investigated with a superconducting quantum interference device (SQUID).