Objective To investigate the associations between unilateral or bilateral hearing loss and 12 chronic diseases as well as multimorbidity among the oldest old in China, and to identify disparities in these associations of left- and right-side hearing loss with chronic diseases. Methods Totally 7 437 people aged ≥80 years old were selected from the Chinese Longitudinal Health and Longevity Survey (CLHLS) 2018 cross-sectional data. With 12 chronic diseases and multimorbidity as outcome variables, the hearing loss as explanatory variable, socio-demographic characteristics, family factors, and lifestyle as covariates, the correlations of unilateral (left- or right-side) and bilateral hearing loss with chronic diseases and multimorbidity were analyzed using multivariate logistic regression model, and the trend analyses were carried out. Results There were 205 (2.76%), 227 (3.05%) and 3 598 (48.38%) old people with left-side, right-side and bilateral hearing loss, respectively. After adjusting for confounders, the oldest old with left-sided or bilateral hearing loss had a greater risk of multimorbidity compared with those with normal hearing function, with odds ratio (95% confidence interval) of 2.14 (1.58-2.90) and 1.27 (1.13-1.43), respectively, while no association between right-sided hearing loss and multimorbidity was observed (P＞0.05). Trend analysis showed that the risk of multimorbidity increased with hearing loss from none to unilateral and then to bilateral (P＜0.001). Conclusion Hearing loss may be related to the increased risk of multimorbidity in the oldest old, and the risk of those with bilateral hearing loss is higher. More attention should be paid to the prevention and treatment of hearing loss in the oldest old.