The Acre flag is split diagonally from the upper fly to the lower hoist. The upper part is yellow and the lower part green. In the yellow, near the hoist, is located the "lone star" (estrela solitária) that symbolizes the light that guided those who supported the incorporation of the Acre territory into Brazil. Yellow symbolizes peace and green hope, according to José Plácido de Castro, who adapted the ancient design of the revolutionary era to the proposal of Colonel Rodrigo de Carvalho, leader of an earlier revolution in the area. The basic design had been adopted by Don Luís Galvez Rodriguez de Arias. The flag was officially adopted by Governor Epaminondas Jacome.

Acre was constituted as a federal territory of Brazil on 25 February 1904. The territorial governor adopted a revised form of the Galvez-Castro flag as the territorial flag on 15 March 1921, with the direction of the diagonal dividing line and the position of the yellow and green triangles reversed, as at present. It is not clear whether this change was made for the first time in 1921 or if it had already occurred de facto before then. The territory of Acre became a state on 15 June 1962 under federal law no. 4070. Its Constitution, adopted 1 March 1963, states (Title II, Chapter I, Article 8) that "The symbols of the state shall be the flag, hymn, and arms that were adopted by the Independent State of Acre."

A new coat of arms was adopted by resolution of 24 May 1922 by Governor Jacome and General Secretary Francisco de Oliveira Conde.

About 1978 I asked for information about the Acre flag. Profesor Arthur Luponi sent me a printed construction sheet of the flag showing the ratio as 7:10. [The image above is based on this construction sheet - ed.] Based on that, I believe that the proportion of the first flag was 11:20 but when adopted as the territorial (and later state) flag, it was in the proportions 7:10 like the national Brazilian flag. Yes, Whitney Smith gives 11:20 as the proportions, but he must be confusing the current flag with that of the first decree.

The decree of 15 March 1921 signed by Governor Epaminondas Jacome adopting the territorial flag is transcribed in Luponi's article in the Flag Bulletin giving the proportions 11:20, but was changed later.

At the on-line edition of Jornal A Tribuna is a story from August 2002 to the effect that the Acre state government is building a 60 meter (197 ft) flagpole in connection with the centennial of Acre's definitive joining of Brazil. The pole will fly a 12 x 17 meter (39 x 56 ft) flag. This news story supports a 7:10 ratio for the Acre state flag, since 12:17 is, for all practical purposes, 7:10.