This research aimed to determine the factor that had the most significant contribution to students' motivation to learn English and the predictors of each element in the L2 Motivational Self System (L2MSS) model in the Vietnamese context. Quantitative results were collected from 231s to year English major students via the survey questionnaire adopted from Taguchi et al. (Z. D & ouml;rnyei, E. Ushioda (eds) Motivation, language identity and the L2 self, Multilingual Matters, Bristol, 2009). Multiple regression analyses revealed the significant contributions of the three main elements of D & ouml;rnyei's L2MSS model (Ideal L2 Self, Ought-to L2 Self, and L2 Learning Experience) to students' Intended Learning Efforts. The Ideal L2 Self plays a decisive role in encouraging and promoting students' efforts to learn English within the Vietnamese EFL context. The findings also highlight the predictors of L2MSS elements. Specifically, Instrumentality-Promotion, Attitudes to L2 Community and Culture, and Ought-to L2 Self significantly influenced the students' Ideal L2 Self. Meanwhile, Instrumentality-Prevention, Family Influence, and Ideal L2 Self had a notable impact on the students' Ought-to L2 Self. Data analyses further revealed the reciprocal influence between students' Ideal and Ought-to L2 Selves and their L2 Learning Experience. The causal relationship among L2MSS elements underscores that students' selves are embedded in socio-cultural and educational contexts, shaped by and shaping these external influences. This study confirms the relevance of D & ouml;rnyei's (Z. D & ouml;rnyei, E. Ushioda (eds) Motivation, language identity and the L2 self, Multilingual Matters, Bristol, 2009) L2MSS model in understanding students' motivational selves in the Vietnamese EFL context and offers recommendations for future research.