Yingluck sent her lawyer to seek permission from the court to take her son to visit Japan on an education field trip in the later part of this month.
The court decided that Yingluck did not have any emergency cause for leaving the country.
Yingluck is facing a trial of alleged negligence of duty related to the rice-pledging scheme.
Earlier this month, she asked the court for permission to leave the country to visit the European Parliament to exchange opinion on Thailand’s situation as invited by some European parliamentarians but the court rejected her request.