The tourist sent the glass shard along with a letter of apology to the Tourism Authority of Thailand, reports said in Bangkok on Sunday, quoting Chakarat Chitrabongs, a senior official of the Thai Ministry of Culture.
The tourist, who signed his name as Juergen Z, reportedly wrote that he had found a tiny glass tile chipped off a wall in Bangkok's Wat Phra Kaew, or Temple of the Emerald Buddha, while visiting it two or three years ago.
He pocketed the tile after his tour guide told him he could take it home as a souvenir, Chakarat told a Thai newspaper.
"Whether I have been cursed or not, I don't know, but something supernatural has been occurring... and I have faced only bad luck, both in my personal and work life," the letter said.
"So I am sending this tiny piece of glass back to you with this letter and I will send money as donation to the temple to apologise and try get rid of my bad luck," he wrote.
The 221-year-old temple is a popular tourist spot in the Thai capital.