A nitridated Ru/B4C multilayer with period of 3.0 nm and 80 bilayers were fabricated to study thermal and temporal stability. The multilayer was annealed from room temperature to 490°C, and the in situ X-ray measurements showed that the reflectivity remains mostly unchanged up to 300°C. An essential drop of the reflectivity occurred at 490°C with significantly increased interface roughness. A new layered structure with larger thickness than the original multilayer started to appear at 400°C. The nitridated Ru/B4C multilayer remains intact after two years of storage in air, which demonstrated a very good temporal stability.