The purpose of this study is to examine the effects of science instruction using argumentation, with Tolumin`s structure of argument, on students` learning motivation and scientific attitude. In the instruction, well-structured problems selected to be argument, in which interactions among students are stressed. The subjects were classified into two groups: One group is composed of sixty-seven students (experimental group) who were participated in solving processes of the scientific argument tasks, and the other is composed of sixty-nine students (comparative group) who were participated in the traditional teaching method. The results of this study implied that experimental group has a positive effect on students` learning motivation and scientific attitude.