The original statue would have stood 4m-5m in height, experts estimate.
His achievements include the massive wall built across the width of northern Britain which bears his name.
Ruling Rome from AD117 to AD138; he was known as a great military administrator and is one of the so-called "five good emperors".
So far, the excavators have unearthed the head, foot and part of a leg.
But they are hopeful other parts of the statue may be uncovered in coming weeks.
The foot is 80cm (31.5 ins) long, the leg - from just above the knee to the ankle - is nearly 70m (27ins) long. The head, which is almost intact save for its broken nose, also measures 70cm (27 ins).
The pieces of this giant monument to Hadrian were found about 5m below ground, among the buried ruins of a bath house on the site Sagalassos, an ancient mountaintop town in southern Turkey.
The statue dates to the early part of Hadrian's reign. The elaborate decoration on the sandal suggest he was depicted in military garb.
The discovery was made by archaeologists from the Catholic University of Leuven in Belgium, who have been investigating the site since 1990.
Marc Waelkens, director of the excavation, said this was one of the "most beautiful depictions" of the emperor ever found.
Born in AD76 into a well-to-do family in Italica, near modern Seville, Spain, Hadrian presided over a period of relative peace and prosperity in the Roman Empire. He erected permanent fortifications along the empire's borders in order to consolidate Roman power.
Güncelleme Tarihi: 10 Ağustos 2007, 09:08
The northernmost extent of this frontier is still standing: Hadrian's Wall runs across the width of northern Britain, from Wallsend to the Solway Firth. It was built to repel attacks by Caledonian tribes.
The bath house in which the statue was found was destroyed by a major earthquake sometime between the late sixth and early seventh centuries AD.
The statue was originally created in pieces, which were then slotted into place to create an imposing monument to the emperor.
It is these constituent parts that are now lying on the floor of the wrecked bath house: when the building collapsed, the statue fell apart along its joins.
In the last few days, the team has also discovered marble toes with dowel holes to fix it to a long dress belonging to another huge statue which may be of Hadrian's wife Sabina.
The inhabitants of Sagalassos had special affection for Hadrian. He officially recognised it as the "first city" of the Roman province of Pisidia and made it the centre for an official cult in the region which worshipped the emperor.
These administrative changes attracted thousands of visitors during imperial festivals, boosted trade and, in turn, prosperity.
"As a kind of thanks to the emperor, there were private and public monuments to Hadrian erected throughout the city," Marc Waelkens told the BBC News website.
A sanctuary, or temple, to Hadrian was built in the southern part of Sagalassos.
And in a monumental fountain next to the bath house, archaeologists have found part of a gilded bronze statue of the emperor, paid for by one of Sagalassos' most prominent families.