Lightweight alloys such as aluminum alloy and magnesium alloy have garnered significant attention due to their widespread use in various industries, including aerospace, automotive, and marine applications. These applications usually require excellent corrosion performance of the alloys. Laser surface treatment (LST) has emerged as a promising surface modification technique to enhance the corrosion resistance of these alloys for its automation and reproducibility. In this study, the effects of LST based on a nanosecond pulsed laser on the corrosion resistance of lightweight metal alloys, specifically AA6061 and AZ31, were studied. LST was performed underwater, using the nanosecond laser and without using a protective coating or layer on the workpiece. The corrosion behaviors of these alloys were analyzed through electrochemical tests, including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) measurements. The results demonstrated that LST significantly improved the polarization resistance, and higher laser power intensities led to increased corrosion resistance and reduced corrosion rates. This enhancement in anti-corrosion performance is attributed to the formation of a protective oxide layer on the surface, acting as a barrier against corrosion. The findings underscore the potential of laser surface treatment as a viable technique for enhancing the corrosion resistance of lightweight metal alloys.