It is revealed that nickel nanopowder synthetized by thermal decomposition of nickel formate in hydrogen flow is pyrophoric at 20⁰C; the nanopowder is not pyrophoric in dehumidified air at temperatures lower than  – 3⁰C. However, its surface reacts with the air; the process stabilizes nickel nanopowder at room temperature. It is shown that nickel nanopowder obtained from nickel formate in argon at 209⁰C and the subsequent processing of the nanopowder in hydrogen flow during the specified time interval allows controlling the level of pyrophoricity and the mean specific surface of the nanopowder.