The microstructures and corrosion behavior of the hypoeutectoid U-Nb alloy laser welded joint were investigated by OM, SEM, XRD and electrochemical analysis. The results indicate that the grain size of the weld zone of the hypoeutectoid pearlite U-Nb alloy is about 50 μm and the weld zone is only composed of α′ martensite with orthogonal crystal structure. After immersion in 3.5%NaCl solution, the corrosion potential of weld metal is ~400 mV lower than the substrate’s, and the corrosion couple forms between weld metal and the rest of the welded. The results of surface morphology and linear polarization show that the corrosion process of the welded joint includes galvanic corrosion and self-corrosion while galvanic corrosion behavior is the dominated. The corrosion current of welded joint is about 3 times higher than that of the substrate and 10 times higher than that of the weld metal. The overall anti-corrosion property of welded joint is depressed. The corrosion is uniform