BackgroundPrevious studies have shown that type 2 diabetes mellitus (T2DM) can cause sarcopenia; however, these conditions may have a bidirectional association. This study aimed to explore the longitudinal association between possible sarcopenia and new-onset T2DM.MethodsWe conducted a population-based cohort study using nationally representative data from the China Health and Retirement Longitudinal Study (CHARLS). This study included participants aged ≥ 60 years who were free of diabetes during the baseline survey of CHARLS (2011 to 2012) and were followed up until 2018. Possible sarcopenia status was defined according to the Asian Working Group for Sarcopenia 2019 criteria. Cox proportional hazards regression models were used to evaluate the effect of possible sarcopenia on new-onset T2DM.ResultsIn total, 3,707 individuals were enrolled in this study, with a median age of 66 years; the prevalence of possible sarcopenia was 45.1%. During the 7-year follow-up, 575 cases (15.5%) of incident diabetes were identified. Participants with possible sarcopenia were more likely to have new-onset T2DM than those without possible sarcopenia (hazard ratio: 1.27, 95% confidence interval: 1.07–1.50; p = 0.006). In subgroup analysis, we found a significant association between possible sarcopenia and T2DM in individuals aged < 75 years or with a BMI < 24 kg/m². However, this association was not significant in individuals aged ≥ 75 years or with a BMI ≥ 24 kg/m².ConclusionsPossible sarcopenia is associated with an increased risk of new-onset T2DM in older adults, especially in individuals who are not overweight and aged 75 years or younger.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12877-023-04104-9.