Sainyabuli is the capital of Sainyabuli Province in Laos. It lies in the country's northwest, on Route 4, which together with Route 13 connects the town to Luang Prabang, roughly 80 kilometres to the northeast by road.
The town also lies near the Thai border, which is reached across the Luang Prabang Range to the southwest. Sainyabuli Airport is located southwest of the town.