In this study, the effect of ‗explicit reflective guided inquiry‘ (ERGI) laboratory practical activities on first-year physics students‘ understanding of nature of science (NOS) and academic performance is investigated. Ninety seven students participated in the study and were systematically assigned to the control group that did recipe-based practical activities and the experimental group that did ERGI laboratory practical activities. Both groups had to answer the same explicit reflective questions on an aspect of NOS at the end of each practical session. Data were collected using the VNOS Form-C questionnaire, focus group interviews, explicit reflective questions, combined practical and theoretical year-end examinations. Using blind scoring, students‘ views were classified as informed, mixed or naïve for each aspect of NOS. The percentage of informed views was larger for the experimental group in each of the seven NOS aspects. Overall, the percentage informed views in the experimental group was larger by a statistically significant margin of 10 percentage points (p = 0.008). The largest differences were observed in the tentative nature of science, the distinction between theory and law, and the role of imagination and creativity. Additionally, males showed more informed NOS understandings than females, while low achieving students were better informed than high achievers, but the differences were not statistically significant. The experimental group did not perform any better than the control group in the practical and theoretical year-end examinations. Therefore, this study demonstrated that ERGI laboratory practical activities activities enhanced first-year physics students‘ understanding of NOS but not their academic performance.