The Prince is touring the sites of Russia's second city which is known for its ornate palaces and elaborate churches and is celebrating its 300th anniversary this year.
He has visited the chapel where the remains of his distant ancestors - the murdered Tsar Nicholas II and his family - were interred in a historic ceremony five years ago.
His visit comes after President Vladimir Putin's recent state visit to Britain - the first by a Russian leader for nearly 130 years.
During his stay, Prince Charles will also return to the Piskarevskoye cemetery for a wreath laying ceremony.
The site is home to the graves of 500,000 people who died in the 900-day Nazi siege of Leningrad, as the city was previously known, during the Second World War.
His last visit was in 1994 when he became the first member of the royal family to visit St Petersburg for 100 years.Links between the British Royal Family and Russia were severed after the Bolsheviks executed Tsar Nicholas II during the Russian revolution in 1917.