The study investigated the relationship of high school students' understandings about nature of science (NOS) aspects and their argumentation skills in relation to two controversial socioscientific issues. The study was conducted in five schools selected from different geographical areas in Beirut, Lebanon. Participants were 219 grade 11 students. Students in all the schools were administered a survey that consisted of two scenarios that addressed the controversial socioscientific issues about genetically modified food and water fluoridation. The two scenarios were followed by questions relating to argumentation and NOS. The study used a mixed methods approach where quantitative and qualitative measures were employed. Analysis involved participants' views of the target NOS aspects (subjective, tentative, and empirical) and their argumentation components (argument, counterargument, and rebuttal). The Pearson analyses showed strong correlations between the counterargument, compared to argument and rebuttal, and the three NOS aspects. Further, the chi-square analyses showed significant differences in participants' argumentation skills and NOS understandings between the two scenarios. Qualitative data from questionnaires and interviews further confirmed these findings. Two central implications for the teaching of NOS and argumentation skills were discussed in terms of highlighting the role of counterarguments and considering contextual factors that involve issue exposure and familiarity, prior content knowledge, and personal relevance. (Contains 8 tables.)