This study investigates the effects of teacher portfolio construction upon in-service English language teachers' perceived teaching competencies. With the participation of six non-native teachers, data were collected through questionnaires and semi-structured interviews conducted before and after a sixteen-week teacher portfolio construction program. Analyses of the data through descriptive statistics and inductive content analysis revealed that the teachers' perceptions related to their teaching competencies were quite high prior to the portfolio construction process. After the process, however, decrease was observed in the teachers' perceived competencies. Findings also showed that the portfolio construction program was effective for the teachers' in that the process led them to become more self-evaluative, thus reflective and realistic about their competencies.