The long-necked herbivore stretched 27 meters (88 feet) and weighed about 27 tonnes, according to a study published in the journal Scientific Reports.
It probably roamed what is now Thailand between 100 and 120 million years ago and is the largest ever found in SoutheastAsia, researchers said.
They estimated the new dinosaur had the same heft as nine adult Asian elephants.
"Our dinosaur is big by most people's standards -- it likely weighed at least 10 tonnes more than Dippy the Diplodocus," said lead researcher Thitiwoot Sethapanichsakul, referring to the enormous composite cast previously on display at London's Natural History Museum.
The Thai PhD student called the newly discovered sauropod "the last titan" because it was unearthed in one the youngest rock formations where dinosaurs are found in Thailand, according to University College London.
