"This giant weighs 11.3 kilos (24.9 pounds)," Khalil Semhat told the AFP news agency at his farm near Tyre, 85 kilometres (50 miles) south of Beirut.
"I've been working the land since I was a boy, and it's the first time I've seen anything like it."
Mr Semhat, 56, said he had to ask for help from a friend to get the huge vegetable out of the ground. He insisted that he had used no fertilizer or other chemicals to produce it.
Mr Semhat said he hoped his potato will be recognized as the heaviest potato in the world.
The current world record, as recorded in the Guinness Book of Records, is held by K Sloan of the Isle of Man in the United Kingdom for a potato weighing a mere 3.5 kg (7 lb 13 oz). 2008 is the International Year of the Potato, a project sponsored by the United Nations which aims to focus attention on the importance of the vegetable in providing food security and alleviating poverty.