The purpose of this study was to investigate eighth grade students' mathematical communication competency, affective characteristics, and the differentiation in affective characteristics across their communication competency levels. The mixed method sequential explanatory design was used. The quantitative data were collected from 140 students through Mathematical Communication Competency Measurement Tool and Affective Domain Scale. The qualitative data were collected from 31 students, who represent students across all competency levels, through semi-structured and clinical interviews. The results showed that main difficulties of students, whose competency was level-0 or below, were making sense of statements/questions, explaining ideas about the problem. The students, whose competency level was level-1 and level weighted-1, had challenges in explaining a mathematical result or presenting a verbal/written justification. Finally, self-efficacy, anxiety and openness to problem solving of students, whose competency was level-0 or below, differed significantly from other students.