Founded in 1892 in Santiago de Chile, the Liceo de Aplicacion was created to educate boys, with the purpose of being a teacher training place for students of the Instituto Pedagogico (the main teacher training institution for secondary education between 1889 and 1981). However, it is a little-known fact that this emblematic school also educated female students. The aim of this paper is to analyze the characteristics and implementation of the first coeducation project in the history of Chilean public secondary education, from the case of the Female Section of Liceo de Aplicacion. Methodologically, this paper is based on the analysis of the documentation available in the School Archive of the Liceo de Aplicacion and other sources. The paper demonstrates that during the first years of the 20th century the education authorities implemented a coeducation project in the Liceo de Aplicacion, which allowed the admission of female students as well as offering them an education on equal terms to male students. However, female students and professors criticized and resisted this coeducation project, which is demonstrated by the demand of teachers to teach Domestic Economy, a "feminine subject". The above-together with other factors-caused the Female Section to finally become independent and, with this, reaffirm its character as a female-exclusive school.