The current study aimed at examining the effects of subtitled films on the vocabulary development of English as second language (ESL) students. To able to achieve this aim a mixed methods research design was employed. For the quantitative part a quasi-experimental design was implemented through a quantitative research approach. For the qualitative part, after the treatment phase interviews were carried out with the participants in the experimental group. Accordingly, two groups were of focus: control and experimental. One group watched English films with subtitles and the other watched the same films without subtitles. A pre-post test was administered in which the pre-test was employed as a diagnostic test to see whether the participants vocabulary knowledge was similar and the post test was administered to reveal whether the student participants had improved their vocabulary knowledge. Thirty ESL students preparing for their O level exams constituted the participants. The findings revealed that films improve vocabulary knowledge. However, when the performances of both groups were compared it was revealed that the group who watched the films with subtitles performed better than the group that watched the films without subtitles. In other words, it was revealed that, the use of watching films with subtitles intensively affected ESL students’ vocabulary knowledge. Furthermore, this study revealed that ESL students have positive attitudes towards watching films in language classes in general, and in vocabulary classes in particular.