Uniform core@shell cobalt nanoparticles (NPs) embedded into mesoporous silica (Co@m-SiO2) were prepared by a simple two-step procedure. Metallic cobalt NPs stabilized by sodium citrate and a nonionic polymer poly(vinylpyrrolidone) were coated by a homogeneous silica shell by using a modified Stöber protocol. In the second step, the mesoporosity of the shell was produced through a pseudomorphic transformation by using cetyltrimethylammonium bromide in alkaline media. An in situ XRD study performed in air on the resulting Co@m-SiO2 solid revealed that this new material is stable under ambient conditions and even resistant towards oxidation up to 450 °C. It is noteworthy that only 30 % of the Co3O4 phase is detected after air treatment at 550 °C. As a result, the core@shell morphology is preserved even at 700 °C in air, which shows the stabilization effect and sintering resistance of this type of structure.