In 1989, the military junta officially changed the English version of the country’s name from Burma to Myanmar, along with changes to the English versions of many place names in the country, such as its former capital city from Rangoon to Yangon. This decision has, however, not received legislative approval in Burma. The official name of the country in the Burmese language, Myanma, was never changed. Within the Burmese language, Myanma is the written, literary name of the country, while Bama or Bamar (from which “Burma” derives) is the oral, colloquial name. In spoken Burmese, the distinction is less clear than the English transliteration suggests.

Source: http://en.wikipedia.org/wiki/Myanmar