Today’s world demands the use of the English language in different areas of knowledge. Besides, the increasing use of technology in educational settings (Zandi et al, 2014; Murray, 2014) encourages teachers to restate their professional development by focusing their efforts on becoming proficient in the use of Information and Communication Technologies (ICTs) in language lessons (Chen et al, 2009). Following the previous ideas, this qualitative action research project intended to describe Content-subject teachers’ EFL oral behavior when blended learning was implemented in a professional development course; and to determine the influence of Blended learning in EFL oral skills behavior. The participants were seven content- subject teachers from a private school in Huila, Colombia. Data were gathered via in-depth interviews, class observations, video recording analysis, teacher’s reflection, students’ artifacts and a survey. The data were collected during the implementation of an English blended course, in which twelve lessons were divided into six face-to-face sessions and six online meetings. The findings suggest that EFL oral skills behavior is connected with use of vocabulary, use of body language, pronunciation and intonation patterns, production of chunks of language, monitoring oral production and, motivation and engagement. Besides this, Blended learning influenced participants’ oral production too.Keywords: blended learning, content-subject teachers, EFL2 oral skills, professional development.1. Educators who teach content subjects in Spanish2. English as a Foreign Language