Police spokeswoman Amalia Ignatencu told The Associated Press the three Britons were hit by a vehicle driven by a 20- year-old man today afternoon near the village of Agighiol.
She said a 56-year-old suffered a fatal heart attack, and another was airlifted to a hospital in the city of Galati with head and chest injuries.
Another was hospitalized in the nearby city of Tulcea.
The injured men are both 60. Ignatencu said the driver, who "didn't keep his distance" from the cyclists, has been detained for questioning.