Withoon Jungphan, 22, of Ubon Ratchathani, returned the bag along with 5 million yen, 23,440 baht, a Louise Vuitton belt, two red gems and other valuables, worth about 1.5 million baht in total, to Thanisara Attarit, 47, at the FM 91 traffic radio station on Tuesday (Jan 14) afternoon.
Ms Thanisara is deputy manager of an office rental firm and owner of a Thai restaurant in Japan.
She and a Japanese colleague arrived at Don Mueang airport and took a taxi to Manthana housing estate in Chaeng Wattana area on the night of Jan 13.
She later realised she had left a bag in the cab.
Mr Withoon said the two passengers hailed his taxi at terminal 2 around 7pm on Jan 13. They had several pieces of luggage and golf bags. Most went in the trunk and some on the front seat of the cab. The two passengers sat in the back.
After dropping them off at the housing estate, another woman hailed his taxi on Soi Tivanon 3. She went to sit in the front seat and noticed a small bag on the floor. It had been forgotten by his previous fare.
He thought it probably contained clothes and decided to drop his new fare, who was heading to Silom, before taking the bag to FM91 traffic radio station to help find the owner.
However, he had several more passengers and then received a call from the radio station asking about the forgotten bag. He drove to the station and handed it over around 9pm.
When staff opened the bag, he saw it contained cash and other valuables, Mr Withoon said.
Ms Thanisara said that around 8pm she was shocked to suddenly realise she had left a bag in the cab containing cash and other items, some of it intended for a golf competition to strengthen relations between Thai and Japanese businesspeople.
She thanked the taxi driver for returning the bag and rewarded him with 23,440 baht cash, the same amount of Thai currency that was in the bag.