This study used a mixed-methods approach to investigate Iranian EFL learners' attitudes towards demotivating factors which may hinder their success in a language learning course. In the quantitative phase, a sample of 337 undergraduate students from universities in Mashhad, Yazd and Gonabad completed a 34-item questionnaire. They also completed open-ended questions which asked them to reflect on any previous EFL (English as a foreign language) learning experiences which had negatively affected their language learning motivation. In the qualitative phase, 15 students participated in semi-structured interviews, and 23 in focus group discussions. Quantitative data were subjected to principal component analysis (PCA), which subsequently revealed the presence of six demotivating factors, including lack of success, insufficient technological facilities, teacher's competence, teaching method and behaviour, lack of interest, class materials, and the class environment. Results of the study revealed that the qualitative findings were compatible with the factors that emerged from the quantitative phase.