This study explores Bhutanese in-service science teachers' conceptions of the nature of science (NOS) by using the Understanding Nature of Science (UNOS) questionnaire. The 15, two-tiered items focus on the five aspects of NOS: (1) scientific knowledge; (2) scientific theories and laws; (3) scientific method; (4) scientists' work; and (5) scientific enterprise. The data were analyzed using descriptive statistics and ANOVA tests. The findings revealed that a majority of the inservice science teachers possessed a naïve or uninformed conception of NOS on some aspects of scientific theories and laws, scientific methods, scientists work, and scientific enterprise. A one-way analysis of variance indicated that there was statistically no significant difference on the level of conception of NOS for the in-service science teachers' based on their teaching subject (F[2, 75] = 0.44, p = 0.064) at p = 0.05. The findings of this study may inform the relevant stakeholders about the current state of the in-service science teachers understanding of NOS and suggest further research in better understanding how Bhutanese teachers model NOS in their classroom teaching.