Written feedback provided by teachers has proven to be important in helping students improve their writing skills. This study was carried out with the purpose of finding out what five teachers and 25 students of a Public Mexican University believed about written feedback and its impact on students' writing skills. A mixed-method research with a quantitative analysis of my participants' responses and a qualitative analysis or interpretations of beliefs was used. In order to obtain data, four different questionnaires were administered: two for teachers and two for students. Apart from the questionnaires, those teachers were also asked to mark a text portion analysis by following some particular directions. The results of this study showed that teachers and students believe written feedback provided by teachers helped students improve their writing skills. Both parts, teachers and students, believe that students have shown improvement in grammar, lexis, cohesion and coherence, accuracy and fluency. Besides, the study also showed that most of the students are likely to take into account their teachers' feedback with the intention of improving their writing skills.