<p>Loneliness has long been recognized as a key predictor of depression in older adults, and both are related to sleep quality. However, to this day, less is known about whether sleep quality mediates their relationship. This study aimed to examine the relationship between loneliness, sleep quality, and depressive symptoms, and to further explore whether sleep quality mediates the relationship between loneliness and depressive symptoms. Using the random cluster sampling method, 1016 permanent residents aged 45 and above in Ankang City, Shaanxi Province were selected. The relationship between loneliness, sleep quality, and depressive symptoms was analyzed using binary logistic regression, and the mediating role of sleep quality between loneliness and depressive symptoms was analyzed using the PROCESS macro in SPSS 25.0 software. The average age of the participants in this study was 60.39 ± 8.50. Regression analyses showed that individuals with loneliness (OR 7.161, 95%CI: 4.889–10.490, P &lt; 0.001) and those with poor sleep quality (OR 4.777, 95%CI: 3.301–6.913, P &lt; 0.001) were more likely to experience depressive symptoms than individuals without loneliness and with good sleep quality. This study also found a significant mediating effect of sleep quality between loneliness and depressive symptoms [effect value = 0.066, bootstrap 95% CI: (0.037, 0.093)] with an effect size of 13.31%. Loneliness may lead to reduced sleep quality in individuals, which in turn may lead to or exacerbate depressive symptoms. Therefore, this study highlights the importance of assessing and improving sleep quality in lonely people.</p>