This study is conducted to identify the key factors and propose a roadmap for successful lean transformation in Vietnamese manufacturing firms. Eight managers of two companies having successful lean performances and two lean experts from university and consulting company are invited to participate in semi-structured interviews to verify key factors of a successful lean transformation as well as to promote a lean roadmap with tools used for lean transformation in the context of Vietnam. The research results show that 10 key factors promoting a successful lean transformation are Role of management, Involvement and Commitment to change, Balanced scorecard implementation, Corporate vision and values, Corporate culture of change, Persuasive situation for change, Change projects, KPI application, Lean consultants, and Stakeholder communication. The respondents also adopt a roadmap for a successful lean transformation in Vietnamese companies including 3 phases (preparation, implementation, maintenance and improvement) in which 5S, Visual Control, and Work Standardization are the three most remarkable tools for lean transformation.