The 46-year-old - named only as Julie - was held and quizzed by police and FSB secret service officers after the discovery as urgent checks were conducted.
The item was later described by officials as a 'hoax grenade', which the woman - due to check in for a flight to London - said she had bought at a Moscow market.
Security teams at Sheremetyevo Airport detained the woman for interrogation as bomb disposal officers were summoned.
Part of the busy airport was sealed off.
The lookalike weapon showed on a scanner during a compulsory luggage check at a terminal entrance .
The London woman was searched and faced questioning by FSB security service officers before being released and allowed to fly home.
The fake weapon was impounded by Russian airport security officers.