The plane, bound for Turkey’s largest city, was diverted after a piece of paper with “bomb” written on it was discovered in the toilet, a spokesman for Turkish Airlines said.
Nothing was found in the search of the aircraft in Shannon, the Turkish Airlines spokesman said, adding that the plane would take off again to Istanbul.
An airport spokesman said the Boeing 777 touched down without incident and all 209 passengers, plus crew, disembarked safely.
“The incident is now the subject of a follow up investigation from an Garda Siochana (Irish police),” he said.
Turkish Airlines has been targeted with a series of hoax bomb warnings over the last year.