Tenasserim, a commissionership of British Burmah, on the E. side of the bay of Bengal, extending 650 m. from N. to S., with a breadth of from 30 to 80 m., between lat. 10° and 19° 30' N, and Ion. 95° 30' and 99° 30' E., bounded N. by Burmah, E. by Siam, S. by the Malay peninsula, and W. by the bay of Bengal, gulf of Martaban, and the administrative division of Pegu, from which last it is partly separated by the river Salwen; area, 46,730 sq. m.; pop. in 1872, 576,765. The country is divided into the districts of Amherst, Tavoy, Mergui, Shwe-gyen, Salwen, and Toungoo (which till recently was a division of Pegu); and the chief towns are Amherst, the capital, Maulmain, Martaban, Tavoy, Mergui, and Tenasserim. The sea coast of Tenasserim is about 500 m. in length. S. of lat. 11° 40' it is bold and rocky, while further N. it is flat and much indented with bays, creeks, and estuaries. Along its whole extent are situated islands which appear from seaward to form part of the shore. Those lying S. of lat. 14° 40' N. are known colleetively under the name of the Mergui archipelago. They vary greatly in form and dimensions, and are mainly situated from 30 to 80 m. off the shore.

The most important island on the coast, however, is Balugyun, opposite the town of Maulmain, 17 m. long and 8 m. broad. The territory of Tenasserim is generally hilly or mountainous. It is intersected by numerous rivers, particularly toward the north, the principal being the Salwen, Attaran, Tavoy, and Tenasserim. The area of the basins of the rivers is estimated at about 14,000 sq. m. The E. boundary is formed by a range of wooded mountains varying in height from 3,000 to 4,000 ft. above the sea. In the north there is a separate range, about 2,000 ft. high, covered with bamboo jungles. There are extensive plains and fertile valleys lying upon the banks of the northern rivers. The staple productions are rice, cotton, sugar cane, indigo, and tobacco; and wheat, nutmegs, spices, and dye stuffs are raised. The country is exceedingly rich in valuable forest trees, prominent among which is the teak. Nearly 380 different varieties of timber have been enumerated. The timber forests are under strict and careful governmental control. Tin is mined, and iron, gold, and antimony are also found. Coal of good quality has been discovered in several places. The climate is considered remarkably healthful, the rate of mortality among Europeans being little more than it is in Europe under like circumstances.

The thermometer rarely rises above 90°, the average being 77°. The rainy season begins in the S. part of the territory about the 1st of May, and at Maulmain a month later; the rainfall is much greater toward the north, where it is estimated at 200 in. a year. The average for the whole country is not less than 100 in. - The population comprises Burmese, Peguans, Siamese, Karens, Seelongs, Hindoos from the Coromandel coast, half-caste Portuguese, Chinese, a few American missionaries, and the English officials and traders. The Burmese and Peguans are the most numerous; the Siamese are principally settled in the neighborhood of the Tenasserim river. The chief manufactures are cotton and silk goods, coarse pottery, and iron cooking vessels. Ship building is largely carried on at Maulmain, and to a less extent at Mergui and Tavoy. These three places are the principal ports of Tenasserim, in regular steamship communication with each other and the Indian peninsula. The chief exports consist of rice, tobacco, gambir, ivory, edible birds' nests, and teak timber. - The Portuguese visited the territory, which forms the Tenasserim division early in the 17th century; and in 1687 some English were massacred at Mergui, the country being then a dependency of Pegu. It afterward became subject to Siam, from which power it was taken about the middle of the 18th century by the Burmese, who held it till it was annexed to British India at the termination of the Burmese war in 1826. From the long unsettled state of the country, the entire population at that time amounted only to about 30,000; and its subsequent rapid increase is attributable to the security for life and property afforded by British rule.

The town of Tenasserim, on the river of the same name, in lat. 12° 2' N, Ion. 98° 55' E., was formerly the capital, but is now largely in ruins.