San Juan is a small Late and Terminal Classic transshipment point on the north end of Ambergris Cay, Belize. It was well situated to have participated in the Maya maritime trade network that served large population centers on Corozal and Chetumal bays and those communities linked to these bays by the New River and Rio Hondo. A sample of Terminal Classic obsidian was analyzed using visual, x-ray fluorescence, and neutron activation techniques. Although the bulk of the obsidian derives from El Chayal in Guatemala, as is common during the Terminal Classic in northern Belize, an unusually large proportion comes from Mexican sources.