A Second World War-vintage smoke bomb was discovered at the popular Knettishall Heath reserve, near Thetford.
A walker discovered the device in woodland at the Suffolk Wildlife Trust-owned reserve on Thursday.
A bomb disposal unit, based at Colchester, was dispatched.
St Edmundsbury police also attended.
The two-inch mortar smoke bomb, which contained no explosives, was recovered for safe disposal.
An Army spokesman said: “We would encourage the public to raise the alarm if they do have concerns about any suspect items they find and not to touch them.
“It is better to be safe than sorry.”
Last month, an old ordnance found on the beach between Holme and Thornham.
The items, including a Second World War 25lb projectile and flares, was demolished.
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