The design of a highly adhesive, defect-free and low-temperature sol-gel coating for the protection of magnesium alloys is desirable yet challenging. In this study, a novel SiO 2 -based sol-gel coating is developed by a ring-opening addition reaction. Notably, the integration of individual sol clusters endows the sol-gel coating with a smooth and compact surface morphology, and eliminates the potential corrosion site of the low-temperature-prepared sol-gel coating. Besides, the as-obtained sol-gel coating exhibits excellent metallic adhesion nature. Most importantly, it increases the overall impedance modulus by 27 times than that of the conventional strategy and decreases the corrosion rate from 3.8 ± 0.5 mg cm -2 per day (commercial chromate conversion coating) to 0.5 ± 0.2 mg cm -2 per day.