Thai League 4 (Thai: ไทยลีก 4), commonly known as the T4, was the fourth level association football league in Thailand. In 2009, it was divided into five groups by geographic region. Each group contained 16 clubs except for the Southern Region group which contained 13 clubs. It was sponsored by AIS and therefore officially known as the AIS Regional League Division 2. In 2016, Khor Royal Cup became a trophy for Regional League Division 2.
In 2017, Football Association of Thailand rebranded the league to Thai League 4.