Enhancing the weatherability of bamboo-based products is essential for increasing their application lifespan. In this study, a composite protective coating containing organic and inorganic UV absorbers and a hindered amine light stabilizer (HALS) was investigated for outdoor bamboo scrimber (OBS). The optical properties of weathered coated and uncoated samples were investigated by colorimetry and UV-Vis spectrophotometry. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) were used to determine the physicochemical properties of the coating. The addition of HALS improved the photostability of the coating and preserved the properties of OBS. Compared to resin-coated samples, alicyclic amines in HALS inhibit photooxidation reactions between bamboo lignin and the coating adhesive. This inhibition is critical for maintaining the UV-shielding performance of the coating. We have developed a photostable protective coating for bamboo-based products whose widespread use can significantly help conserve critical forest resources.