Background <p>Sarcopenia, mild cognitive impairment (MCI), and depression could cause great distress in the lives of older adults and frequently co-occur, yet their interrelationships remain elusive. This study seeks to assess the link between sarcopenia and the comorbid MCI and depression in older Chinese, and their longitudinal impact.</p> Methods <p>We used data from the 2015 (wave 3) and 2018 (wave 4) surveys of the China Health and Retirement Longitudinal Study (CHARLS). Cross-sectional analysis of the 2015 data estimated the baseline prevalence of sarcopenia and its comorbidity with mild cognitive impairment (MCI) and depression. Longitudinal analysis of the 2015–2018 data employed multivariate logistic regression models, adjusted for demographic and health covariates, to examine the prospective association between sarcopenia and incident comorbidities; stratified analyses were additionally conducted among obese individuals. To illustrate the impact of sarcopenia on comorbidity onset, Cox proportional-hazards models were fitted to the 2011–2018 (waves 1–4) longitudinal data to estimate the association between sarcopenia and incident comorbidities.</p> Results <p>During the follow-up period from 2015 to 2018, among 2773 individuals, 190 developed comorbidities of mild cognitive impairment and depression. After adjusting for covariates, compared to non-sarcopenic individuals, those with possible sarcopenia (OR = 2.952, 95% CI: 2.104–4.141, <i>P</i> &lt; 0.01) and sarcopenia (OR = 3.105, 95% CI: 2.064–4.670, <i>P</i> &lt; 0.01) were associated with a higher incidence of comorbidity (<i>p</i> &lt; 0.001). Furthermore, we observed that the incidence of comorbidity was 15.38% points lower in non-obese individuals with sarcopenia compared to those who were obese and had sarcopenia. Compared to the normal group, individuals with obesity who had possible sarcopenia exhibited a higher risk of developing comorbidities(OR = 2.411, 95% CI: 1.472–3.946, <i>P</i> &lt; 0.001), and the sarcopenia group had an even higher risk (OR = 7.580, 95% CI: 2.578–22.289, <i>P</i> &lt; 0.001) in the fully adjusted model accounting for age, gender, residential area, education level, marital status, former/current smoking, former/current alcohol use, other comorbidities. However, in the non-obese subgroup, neither possible sarcopenia group (OR = 1.875, 95% CI: 0.858–4.097, <i>P</i> &gt; 0.05) nor sarcopenia group (OR = 1.222, 95% CI: 0.590–2.529, <i>P</i> &gt; 0.05) showed a statistically significant association with the development of comorbidity.</p> Conclusion <p>These findings suggest that sarcopenia increases the risk of comorbid MCI and depression in older adults; however, this association was only observed in obese individuals, with non-obesity status significantly attenuating the risk. These findings suggest that sarcopenia may represent a potential target for preventive strategies, particularly among obese older adults.</p>