英語授課在非以英語為母語的高等教育中早已蔚為風行，過去相關研究雖描述行政主管、教師、教師所遭遇的衝擊與挑戰，但卻常用個別行動（individual action）為主要分析單位，而忽視集體活動（collective activities）的重要性。本研究以Engeström（1987, 1996, 2001）活動理論（Activity Theory）的內部衝突（inner contradiction）概念為框架，假設對象導向（object-oriented）與工具中介（tool-mediated）的活動系統（activity system）改變是因內部衝突而致，試圖探討一所私立大學專業教師與學生的英語授課經驗，並著重指出活動系統內與跨系統間的衝突及影響。研究結果顯示：所有研究參與者都有活動系統內與跨系統間的衝突及改變。以個別活動系統分析而言，學生逐漸從使用取向變成分數取向，而專業教師則逐漸能重視學生需求。雖然兩者改變的動機不同，但在各自教學經驗影響下，卻從未挑戰英語授課的政策。以集體活動系統分析而言，研究並未發現教師與學生在英語授課中設定立即的共同期待，活動系統也沒有質的變化。本文證實活動理論在英語授課研究與教學的可行性，而透過活動系統分析描繪各重要關係人系統內與跨系統間的衝突，也將為未來英語授課的教學與改變奠定基礎。 University settings in non-native English-speaking (NNES) contexts have witnessed the growth of English-medium instruction (EMI). Most prior research sheds light on the challenges and contradictions NNES stakeholders experience by using individual action as a unit of analysis without considering such experiences as collective activities. Drawing on Engeström`s (1987, 1996, 2001) notion of inner contradiction in Activity Theory (AT) that presumes the derivation of change from tensions in the object-oriented and tool-mediated activity systems, this paper explores content instructors` and students` experiences engaging in English-taught programs in a private Taiwanese university. Specifically, the focus identified inner contradictions within and across activity systems and the corresponding consequences. Findings showed that all participants had tensions within and across collective activity systems that could affect the change of these systems. In the individual activity analysis, students tended to adopt a grade, rather than use orientation in object transformations, while content instructors shifted from concern about themselves to recognizing students` needs. Even though the motivation behind initiating change in the activity system may differ, the deep-seated rules about English-only instruction remained unchallenged, with stakeholders` history of learning and teaching being a significant mediator. The joint activity analysis showed no shared object between students and content instructors in adopting EMI and no qualitative change. Such results attest to the usefulness of the AT framework in future EMI research. The discussion of the effects of these contradictions within and among stakeholders through an AT perspective supports future pedagogy and interventionist research in which new practices can be derived from activity system analyses for EMI development.