Sainyabuli is the capital of Sainyabuli Province, Laos. It lies along Route 4 which along with Route 13 connects it to Luang Prabang, roughly 80 kilometres northeast by road and to the Thai border across the Luang Prabang Range in the southwest. A passport control point is located in the area. Sainyabuli Airport lies in the southwest of the town.
The capital stands on the banks of the Nam Hung, a tributary of the Mekong river towards the northern end of the province. The area is allegedly a heartland for military involvement in illegal timber trade.