Teacher professional development (TPD) plays a significant role in better school improvement and student achievements. Research on TPD shows that favorable workplace conditions greatly enhance teachers' teaching knowledge and practice. This research was conducted to find out what workplace conditions principals had created to promote TPD in four schools in a province in Vietnam. The study utilizes multiple-site case study design relating to principal leadership and TPD in those schools. The four key workplace conditions were identified in this study including collaboration, teacher empowerment, supervision and evaluation, and teachers' motivational strategies. Based on the findings, the study offers implications for both research and practice on principal leadership for TPD within and beyond the Vietnamese context.