Scientific argumentation has been greatly emphasized in the National Science Standard due to its ability to enhance students' understanding of scientific concepts. This study investigated the mastery level of scientific argumentation, based on Toulmin's Argumentation Model (TAP), when students engage in individual and group argumentations. A total of 120 students were selected and were first randomly divided into two groups to answer the Scientific Argumentation Test (ScAT). One group of students answered individually, while the other group was allowed to collaborate among group members. The Student Semi Structured Interview (SSSI) and Teacher Semi Structured Interview (TSSI) were also conducted on a selected group of students and their teachers to gather additional information to support the ScAT data. The findings showed that there is a significant difference in the mastery level of scientific argumentation between groups and individuals. Students who participated in group argumentation tend to perform better than those who participated in individual argumentation. However, the mastery level of scientific argumentation for both groups of students was generally unsatisfactory. Therefore, the teaching and learning of science in Malaysian schools need to emphasize more on group argumentative activities to enhance students' mastery of scientific argumentation, which will also their reasoning capabilities and scientific knowledge.