The objective of this present research is to describe the use of the conjunctions, “but” and “however”, in academic essays written in English by Brazilian university students. From this observation, we expect to contribute to the discussions on the practice of teaching English for Academic Purposes - EAP, once insufficient language proficiency was one of the problems identified in international mobility programs. In view of a written production skill and based on theoretical backgrounds of Corpus Linguistics, we have developed a corpus of English learner for analysis - CA – formed by 264 academic essays extracted from the Corpus Inglês para Fins Acadêmicos – CorIFA (DUTRA; QUEIROZ; ALVES, 2017). These texts were written by Brazilian university students with B1 proficiency in English. We also built a corpus of reference - CR - using the same characteristics of the CA, and, after analyzing the excerpts referring to the CR, we compared the writing of these two groups of non-native English-speaking learners. For the drafting of the CR we extracted 31 academic essays written in English by non-native students from the Michigan Corpus of Upper-Level Student Papers - MICUSP. Our theoretical basis relies on the written production ability descriptors of the Common Reference Framework for Languages (2001) to describe the use of conjunctions in academic writing B1 proficiency level. In order to describe the conjunctions “but” and “however”, we use the corpus based grammars Longman by Biber et al (1999) and Cambridge (CARTER; MCCARTHY, 2006), English-language grammars Practical English Usage (SWAN, 2005), The Grammar Book (CELCE-MURCIA; LARSEN FREEMAN, 1999), The English Grammar by Watkins and Porter (2006) and the Cambridge and Wordreference online dictionaries. Through this material, we describe the reason why we consider “but” and “however” expressive grammatical elements and believe in the importance of the proper use of these conjunctions in academic essays. Data extraction was performed using the software AntConc (ANTHONY, 2001), which generates lines according to the word we are looking for. After extracting and analyzing data from both corpora, we compared the use of conjunctions in the beginning of the sentences in order to describe the similarities or differences in writing between the two non-native students. Data found in our analysis from CorIFA have demonstrated that a portion of Brazilian university students uses conjunctions in a wrong way, according to the grammars presented in our theoretical basis. Also, compared to the data extracted from our CR, numbers show that Brazilian students have written conditions below the students who wrote the texts extracted from the MICUSP corpus, pointing to the need for a more in-depth study of English for Academic Purposes in Brazilian universities.