This paper aimed to study of Grade 12 students' understanding of nature of science in learning about atom for peace through science technology and society (STS) approach. Participants were 51 Grade 12 who study in Thongphong high school Vientiane Capital City Lao PDR, 1st semester of 2012 academic year. This research regarded interpretive paradigm. The intervention of STS physics provided 4 weeks of teaching about atom for peace through Yuenyong (2006) science technology and society (STS) approach. Students' understanding of nature of science was interpreted through students' worksheets, participant observation, students' journal writing and informal interview. The findings revealed that students could reflect their ideas related to three aspects of nature of science. This included Socio-cultural embeddedness, empirical basis, and subjectivity. The study has implications for NOS teaching in Lao PDR.