Abstract Aims Sarcopenia has recently been shown to affect quality of life and mortality in patients with diabetes. However, early detection requires an expensive equipment. We hypothesized that the ratio of the creatinine/cystatin (Cre/CysC) could be used as a marker for sarcopenia. Methods We investigated the association between the Cre/CysC ratio and sarcopenia in a cross-sectional study of patients with type 2 diabetes. Skeletal muscle mass (SMM) was estimated by bioelectrical impedance. The skeletal muscle index (SMI) was defined as the appendicular SMM divided by the square of the height. Sarcopenia was defined with SMI and a grip strength. Results We identified 285 patients with type 2 diabetes, of whom 25 (8.8%) had sarcopenia. The Cre/CysC ratio was associated with an increased risk of sarcopenia [odds ratio per 0.01 increment, 1.05; 95% confidence interval (CI), 1.01–1.09] after adjusting for covariates. Receiver operating characteristic curve analysis indicated that the optimal the Cre/CysC ratio cut-off point for identifying sarcopenia was 0.9, with an area under the curve, sensitivity, and specificity of 0.683 (95% CI, 0.573–0.793), 0.80, and 0.48, respectively. Conclusions We recommend the Cre/CysC ratio as a practical screening marker for sarcopenia in patients with type 2 diabetes.