This study aimed to elucidate the relationships among sleep quality, subjective cognitive decline (SCD), and SCD-related functional limitation.The present study used the 2018 Korea Community Health Survey (KCHS) data, which comprise community-based, nationwide representative data collected by the Korea Centers for Disease Control and Prevention. Sleep quality was measured using the Pittsburgh Sleep Quality Index (PSQI). The study population comprised 203,082 persons aged ≥ 19 years.Among 203,082 subjects, 35,892 (17.7%) had SCD and 4,373 (2.2%) had SCD-related functional limitation. Individuals with poor sleep quality (PSQI > 5) were approximately 2-fold more likely to exhibit SCD and SCD-related functional limitation (SCD: Odds ratio [OR] = 1.983, 95% confidence interval [CI] = 1.915-2.054; SCD-related functional limitation: OR = 2.405, 95% CI = 2.158-2.681). Moreover, younger adults showed a greater influence of sleep quality on SCD and SCD-related functional limitation, compared to older adults.Because this study used cross-sectional data, it could not establish a causal relationship among poor sleep quality, SCD, and SCD-related functional limitation.Poor sleep quality might contribute to cognitive and functional decline. The present study showed that, in both younger and older adults, there is a need to identify early stages of cognitive decline (e.g., SCD), as well as to perform intervention to prevent poor sleep quality and cognitive decline.