The artefacts - part of a wooden anchor measuring 150cm long and a damaged urn - "date back to the Roman era", the fire service said in a statement.
They were found at a depth of around 13 metres, during a training session in the coastal town of Livorno, 500 metres from the town's Terrazza Mascagni, a popular terrace and tourist spot on the seafront.
The map below shows the location of the discovery.
After recovering the objects, divers notified the local archaeology authorities, whose experts will carry out a full assessment of the finds.
Firefighters noted that ancient artefacts had been found in the same strait before - however, they are far from being the largest relics which have lain forgotten off Italy's shores for centuries.
In 2015, a Salento fisherman spotted a shipwreck thought to date back to the 12th or 13th century, submerged off the Puglian coast. And in 2012 a 2,000-year-old shipwreck - one of the best preserved - was found off the coast of Liguria, while three years previously, five pristine Roman shipwrecks were found near the small island of Ventotene, part of an archipelago off Italy's west coast.