This paper reports the study of the relationship between foreign/second language (L2) motivation and vocabulary knowledge. A sample was analysed of 195 cadets of a military academy in Saudi Arabia who study English as the only foreign language. The author uses the L2 Motivational Self System (Dörnyei, 2009) to investigate the cadets’ L2 motivation and the vocabulary test “X-Lex” (Meara & Milton, 2003) to measure their vocabulary size. The correlation analysis shows a positive moderate statistical correlation between the students’ L2 motivation and their Vocabulary Size because the Ideal L2 Self, the Language Learning Attitudes, and the Intended Learning Effort had a linear positive relationship with the Vocabulary Size. Nevertheless, the regression analysis reveals that none of these motivational scales is a predictor of Vocabulary Size of the Saudi cadets. Finally, the correlation analysis and the regression analysis highlight a statistically significant correlation between the perception of the Saudi cadets of themselves as competent English users and their L2 motivation as well as their Vocabulary Size.

Keywords: Ideal L2 Self, Language Learning Attitudes, Motivational Self System, Ought-to L2 Self, vocabulary size, X-Lex.