Besao lies at the westernmost part of Mountain Province. It is bounded on the North by Tubo, Abra, on the south by Tadian, on the East by Sagada and on the west by Quirino, Ilocos Sur. It is 28 kilometers away from Bontoc, the capital town of Mountain Province, and 150 kilometers away from Baguio City.
The municipality has a total land area of 19,020 hectares, the second smallest municipality in the province, comprising only of 4.3% of the total provincial land area. However, records of the municipality based on early cadastral surveys, the land area of the municipality is believed to be 38,265 hectares. The conflict in figures is due to the fact that the boundary dispute between Mountain Province and Abra remain unresolved up to the present time.
Besao is 100% forest land. Of the 9,020 hectares, 52.02% are classified as forest reserve, 25.95% are rimber lands while 22.03% are unclassified forest.
There are two pronounced seasons in the municipality, wet and dry. The dry season normally occurs from January to April while the wet or rainy season lasts from May to December. Typhoons normally visit the area during the months of July, August and September. Due to temperature changes, monsoon rains last for weeks, resulting in damage to crops and properties.