[Purpose] To clarify health-related quality of life (HR-QOL) in subjects with mild cognitive impairment (MCI), using EuroQOL (EQ-5D), and to investigate the relationship between HR-QOL and Tokyo Metropolitan Institute Gerontology Index of Competence (TMIG-IC) scores. [Subjects and Methods] The subjects included 25 women with MCI or frail constitutions. A variety of methods were used to assess mental states and activities of daily living (ADL). [Results] EQ-5D scores were significantly lower in the MCI group than in the normal cognitive (NC) group. Among the assessed subscales, the percentages of participants with “moderate problems” during self-care and “moderate and extreme problems” during usual activities were significantly higher in the MCI group. TMIG-IC scores were significantly lower in the MCI group than in the NC group. There was a positive correlation between TMIG-IC and EQ-5D scores in the MCI group. There were also significant positive correlations between instrumental activities of daily living and social roles between EQ-5D and TMIG-IC scores in the MCI group. [Conclusion] TMIG-IC scores may reflect cognitive disorders earlier than BI and FIM. The decline of TMIG-IC scores, especially for IADL and social roles, affects HR-QOL even in the early phases of cognitive impairment.