The purpose of this study is to investigate the effects of small group cooperative learning on lowering the mathematics anxiety and increasing mathematics achievement of middle school students. This study used two classes of second grade in H middle school, located in Chuncheon, Gangwon. The classes were classified by the result of sameness quality tested previously. While one class, as an experimental group received small group cooperative learning, the other class as the controlled group received traditional learning method. The results of this study are as follows: First, this study shows that the experimental group using small group cooperative learning is more effective in terms of relieving mathematics anxiety of students than the controlled group using traditional learning methods. Second, according to this study, the experimental group gained a more positive effect toward continuing relief of mathematics anxiety than the controlled group. This study, however, doesn't show meaningful result on motivating students to get interested in mathematics. Third, this study also show that the experimental group using small group cooperative learning is more effective in terms of mathematics achievement. It implements that application of small group cooperative learning onto mathematics of middle school is one of the important factors to be a desirable teaching-learning model to decrease mathematics anxiety.