Abstract: The present study aimed at investigating the main sources of demotivation among Iranian high school students. The second aim of the study was to investigate the relationship between demotivation and English language learning ability of Iranian high school students. In addition, the possible effect of gender on the relationship between demotivation and English language learning ability of Iranian high school students was examined. To find the major demotivating factors, first, a semi-structured interview was conducted with 20 English teachers and 70 high school students. Then, based on the results from the semi-structured interview and the Kikuchi (2009) and Keivanpanah (2011) studies, a questionnaire including 23 items was developed and pilot tested with 150 similar Iranian high school students in order to validate the questionnaire. The newly constructed questionnaire then was distributed among 600 male and female high school students. Using factor analysis, five factors were extracted: (a) Attitudes toward second language learning, (b) Course books, (c) Teacher Characteristics, (d) Background knowledge, (e) Relevance to Real Life. The results of the Pearson product moment correlation revealed that five demotivating factors namely "Attitudes toward English learning", "Course book", "Teacher Characteristics", "Background Knowledge", and "Relevance to Real Life" were significantly and negatively correlated with English language proficiency of Iranian high school students. Finally, the results of the analysis of covariance indicated that gender had no effect on the relationship between demotivation and English language learning ability of Iranian high school students.
