本文以敘事研究的方式，透過深入訪談，探討一位台灣語言學習者的自主動能（learner agency）與其學習環境之互動。經由敘事訪談（narrative interview）、開放式訪談、半結構訪談以及分析受訪者社群網站發表之文章，本論文意圖呈現台灣語言學習者在不同學習環境中如何表現自主動能。 本研究以受訪者Erin出國留學為分界，共三個階段：第一階段為受訪者出國前（2014/08/25），以敘事訪談（narrative interview）的方式，Erin完整呈現自我對英語的認知與語言學習歷程之掙扎。第二階段為Erin出國以後，藉由開放式與半結構訪談，描繪出Erin在國外求學的經驗，並更深刻探討過去的語言學習歷程。第三階段為Erin回國後(2015/09/17)，再次以敘事訪談的方式，Erin反思英國求學的經驗以及英語在其人生中扮演的角色。 本研究以vam Lier所提之自主動能的三個特色為分析框架，並推衍出兩項申明：其一，台灣英語學習者在正式的語言學習環境中面臨許多挑戰，但學習者仍有表現自主動能的空間，表現方式包括逃避或拒絕學習；其二，學習者若能沈浸於語言習得的環境（foreign language acquisition environments），極有可能脫離正式語言學習環境的框架而成為一個不同於以往的自己。本研究檢視學習者在不同的學習環境中如何展現自主動能，筆者期望研究結果可提供語言教師看待語言學習者一個新視角。 / Drawing on the concept of learner agency, a narrative inquiry was conducted in order to achieve an in-depth, qualitative understanding of the interplay between a Taiwanese learner's exert of agency and various contexts. The study was developed in three phases, and multiple number of interviews were the main instrument for data collection. The first interview was conducted in August, 2014, before the participant, Erin, headed for England to pursue a Master's degree. The following interviews documented her life experiences abroad and further explored her past language learning history. The final interview was conducted in September, 2015 after she came back to Taiwan, in which she reflected on her overall study abroad experiences and the role of English in her life. The findings delineated Erin's English learning story and her agency domestically and internationally. van Lier's proposal of core features of learner agency was used as the analytic framework to discuss Erin's story, and later two assertions were derived from the discussion: (1) Being an EFL learner in the Taiwanese formal educational context may involve many challenges, but the learner still has room to exercise his or her agency-even though this could mean avoiding or rejecting learning, and (2) Fully engaged in a foreign language environment, the learner is likely to break away from the limitations of formal English learning system. The study delineates a close examination on how the language learner interacted with various contexts and demonstrates several considerations TESOL practitioners can take. Based on the findings and the discussion, pedagogical implications as well as suggestions for future research are also provided at the end of the thesis.