OBJECTIVES: To investigate the relationship between sleep and multimorbidity, including the associations between sleep duration and multimorbidity, as well as between sleep quality and multimorbidity. METHODS: Using data from the three latest waves of the Chinese Longitudinal Health Longevity Study (2011, 2014, and 2018), a binary panel regression was conducted to investigate the quadratic relationship between sleep duration and multimorbidity. Subsequently, quadratic fitting and robustness analysis were further utilized to strengthen the verification of this relationship. RESULTS: From 2011 to 2018, the prevalence of multimorbidity increased, with average rates of 0.309, 0.345, and 0.367, respectively. Meanwhile, sleep duration was 7.45, 7.34, and 7.39, but sleep quality showed a declining trend with scores of 3.70, 3.63, and 3.47, respectively. Furthermore, the regression analysis revealed that the odds ratios (OR) for the relationship between sleep duration and multimorbidity, and between the square of sleep duration and multimorbidity were 0.734, with 95 % CI = [0.6272, 0.8582] and 1.016, with 95 % CI = [1.0058, 1.0262], respectively. From the quadratic relationship, it is evident that the multimorbidity among older Chinese adults initially decreases and then increases with long sleep durations. CONCLUSIONS: The multimorbidity was significantly different among individuals with different sleep duration. A U-shaped relationship was observed between sleep duration and multimorbidity, whereby both short and excessive sleep durations were associated with higher rates of multimorbidity. Additionally, a negative association was found between sleep quality and multimorbidity, indicating that higher sleep quality was linked to lower rates of multimorbidity.