The relationship between expressions of a class teacher on the class atmosphere was investigated. First, the frequency a teacher showing six basic expressions was assessed. Secondly, the atmosphere of the class was evaluated and factors that composed class atmosphere were subjected to factor analysis, which indicated that class atmosphere consisted of Unity, Friendly, and strict Factors. A model how expressions of a teacher affected the atmosphere of a class was developed using Covariance Structures Analysis (CSA). The results indicated that the expressions of a teacher had a significant effect on class atmosphere.