Bomb disposal experts raced to the Clydebank tenement to deal with the apparently deadly fragmentation grenade.
Police made the area safe and fire crews were on hand in case the Second World War era grenade exploded.
The shock discovery was made shortly after 5pm on Wednesday.
Two crew from Clydebank fire station spotted the device sitting on the woman's mantlepiece.
Firefighters called police to the building, on John Knox Street, and called in Army bomb squad personnel from Corps in Edinburgh.
A police officer took the grenade outside and placed it on a neighbouring bowling green out of harm's way.
Explosives experts said grenades of its type have a blast range of up to 20 metres, with the ability to spread lethal shrapnel even further.
The grenade had been painted gold and was a gift to the woman, thought to be in her 70s, from her late husband.
However, bomb squad officers confirmed the device was in fact a dummy.
Firefighters found the grenade while carrying out a routine home safety visit at the woman's flat.
Assistant Chief Officer Lewis Ramsay, Strathclyde Fire & Rescue Director of Community Safety, said: "The partnership between the public, the fire service and other agencies is the best defence in the fight against fire."
The Evening Times is working with SFR on its latest fire safety campaign.
Bosses hope as many people as possible will arrange free home fire safety checks – for themselves and for neighbours and loved ones.
Mr Ramsey added: "Firefighters will happily arrange to conduct a free Home Fire Safety Visit at a time suitable for the householder."