The boy, who was French, died on Saturday evening after being stung by the jellyfish, regarded as one of the most poisonous creatures in the world.
According to the Bangkok Post, the attack happened on Had Kuad beach, also known as Bottle Beach. He died on the way to Phangan hospital.
Local police advised tourists to be careful and asked hotels to erect warning signs and prepare emergency packs in case there are any more incidents.
Stings from the jellyfish are fortunately rare.