Writing in the German journal Naturwissenschaften, Eric Buffetaut of France's National Centre for Scientific Research (CNRS) and Dany Azar of the Lebanese University describe two teeth of a massive animal called a brachiosaurus.
A complete tooth was found near the southern city of Jezzine last year and another, incomplete, was discovered there in 1969.
Brachiosauruses were giraffe-necked herbivores which were among the biggest animals that ever lived. They measured up to 25m tip to tail and weighed as much as 50 tons.
The find has been dated to between 130-145 million years ago, when this species was at its peak.
Previous brachiosaurus fossils have been found in North America, Africa and Europe, and also possibly Asia.
Buffetaut and Azar say the teeth are significant because they indicate that the vegetation in the Middle East during the Cretaceous Era must have been abundant in order to support a creature of this size.
Previous evidence of dinosaurs in the Middle East is scarce, being largely limited to fossilised imprints found near Jerusalem and a fragment of tibia uncovered near Damascus.
The Jezzine teeth were found in fluvial deposits that have already yielded amber in which prehistoric insects and plants have been trapped.