Despite extensive research on motivation in English as a Foreign Language (EFL) settings, demotivation within medical education remains underexplored. This mixed-method study employs the Situated Expectancy-Value Theory (SEVT) to investigate the demotivation of English learning experienced by 426 Chinese medical students in their English language learning. Utilising data collected from the adapted English learning demotivation questionnaire, quantitative analysis was conducted through exploratory factor analysis, confirmatory factor analysis, and correlation analysis. Qualitative insights from open-ended responses revealed that the interplay of internal (e.g., lack of self-regulation) and external (e.g., heavy medical course load) factors plays an important role in medical students' demotivation in English. Significant demotivators identified included weak language foundation, heavy workload of medical courses, and lack of self-regulation. A moderate correlation was found between English proficiency and demotivation, emphasising the importance of considering a range of factors, rather than attributing demotivation solely to low English proficiency. The findings extend the understanding of demotivation and reconceptualise the concept through low expectancy of success, reduced value, and high perceived effort cost. Critical insights emphasise the importance of fostering motivating English learning environment in medical education by considering both individual and contextual factors. Implications for educational interventions are discussed.