Sooloo, Or Sulu, the general name of a picturesque chain of islands in the Indian archipelago, known also as the Sooloo archipelago, extending about 250 m. from S. W. to N. E., between Borneo and Mindanao, from lat. 4° 40' to 6° 45' N„ and from lon. 119° to 122° 20' E., separating the Celebes sea on the south from the Sooloo or Mindoro sea on the north; estimated area, 1,300 sq. m.; pop. about 200,000. They lie outside the volcanic belt of the Indian archipelago. The entire number of islands is about 150, most of which are small and uninhabited. There are three large islands: Tawi, near the coast of Borneo; Basilan, close to the S. W. extremity of Mindanao; and Sooloo, about midway between them. Each is about 40 m. long and from 6 to 20 m. wide, richly clothed with tropical vegetation, and rising into peaks of considerable height, those in Sooloo being 2,000 ft. above the sea. The island of Cagayan Sooloo, 140 m. N. W. of the main chain, is sometimes included within the Sooloo archipelago, although it does not properly belong to it. Balambangan island, further west, near Maludu bay in Borneo, is noted for the two unsuccessful attempts of the British to establish themselves there.

It was ceded to England in 1763, but the fortifications were destroyed by the Spaniards in 1775; it was resettled in 1803, but abandoned in 1804. The Sooloo archipelago lies within the influence of the monsoons. The thermometer ranges between 75° and 87°. The chief productions consist of teak and sandal wood, rice, tortoise shell, pearls mother of pearl, fish, tripang, and edible birds' nests. According to Mr. St. John, this archipelago furnishes probably a greater number of valuable oyster beds than any other part of the world. The islands are subject to the sultan of Sooloo, and are governed by numerous petty chiefs. The fortified town of Sugh or Sooloo, on the island of the same name, is the capital and chief port of the group, and carries on considerable trade with the other islands and Manila. Its population is about 6,000, and that of the whole island is estimated at 100,000. The inhabitants are Mohammedan Malays, and were renowned for their piratical habits prior to the repression of piracy in these waters by the Spanish in 1851. They write their, language, which appears to resemble the Philippine tongue, in the Arabic character.