Sithu U Nyun (Burmese: ဦးညွန့်; also spelt U Nyunt; 20 January 1910 – 4 April 1996) was a Burmese development economist, diplomat and intellectual who served as the 3rd Executive Secretary as the head of United Nations Economic and Social Commission for Asia and the Pacific.

[2][3][4] U Nyun was born on 20 January 1910 in Hpa-An, British Burma.

[5] U Nyun served in the Indian Civil Service (ICS) and then as a senior civil servant in the independent Burma government, before joining the United Nations in 1953.

From 1959 to 1973, he was the Under-Secretary General of the United Nations as the head of United Nations Economic and Social Commission for Asia and the Pacific (ESCAP), working directly under Secretaries-General Dag Hammarskjöld and U Thant.

[6] U Nyun was one of many trained and experienced Burmese Indian Civil Service and Burmese Civil Service officers at the time of independence.