Thin nanostructured Ti-BN-based films are known for their excellent mechanical properties and their stability at high temperature in oxidizing atmosphere. In the present work, nanostructured Ti-Al-Si-BN and Ti-Cr-BN coatings deposited on AISI 304 stainless steel by ion implantation have been characterized. To evaluate the oxidation resistance and thermal stability, the coatings were annealed at 900 C in vacuum and in air for 4 hours. The mechanical properties, phase composition and micro-structure of as-deposited and annealed coatings were addressed. The coatings showed a complex multilayered structure and a substantial change of their mechanical properties, due to the new structure and to the phases formed after air annealing.