This paper aimed to analyse the perceptions of university students in relation to the credibility of university instructors according to the tweets posted on their Twitter profiles and the academic motivation that these can generate. Thus, students' perceptions of teacher credibility are affected by what instructors post on their social media profiles. The participants in the study were 166 students from the Faculty of Education Sciences at the University of Seville, carried out using a quasiexperimental methodology for which three Twitter profiles for a university professor were created with professional, social and mixed content. For the analysis of the results, normality and homoscedasticity tests were carried out on the sample to decide which statistical tests to use. The most salient results indicated that students perceived the professional profile as more competent, more caring, and more trustworthy, followed by the mixed profile and, lastly, by the social profile. Positive correlations were also found between students who perceived the university professor as reflected in the professional profile as credible in their academic motivation. The findings and their practical implications for instructors are discussed in terms of how they can incorporate Twitter into their teaching, considering the needs of their students to enhance their learning.