Objective This study aimed to explore the clinical value of serum creatinine Cr / cystatin C CysC ratio as a predictor of sarcopenia for patients with advanced non-small cell lung cancer NSCLC . Method This study included 134 advanced NSCLC patients who were initially diagnosed and treated with chemotherapy in our hospital from January 2019 to January 2022. The skeletal muscle index SMI at the third lumbar level measured by computed tomography CT and handgrip strength were used to diagnose sarcopenia. The linear relationships between serum Cr/ CysC ratio and various nutritional parameters were determined by the Pearson's correlation coefficient and the receiver operating characteristics ROC curve was used to evaluate its predictive value for sarcopenia. Result 46 34. 3% of 134 advanced NSCLC patients were diagnosed with sarcopenia which was found in 35 males 33. 0% and 11 females 39. 3% . Serum Cr/ CysC ratio was positively correlated with with serum albumin value r = 0. 186 P = 0. 032 SMI r = 0. 288 P = 0. 020 and handgrip strength r = 0. 362 P < 0. 001 . The ROC curve showed that the best threshold of serum Cr/ CysC ratio was 0. 872 and its AUC value was 0. 744 95%CI = 0. 660-0. 829 with a sensitivity of 84. 8% and specificity of 61. 4% respectively. The serum Cr/ CysC ratio OR= 0. 005 95%CI = 0. 001-0. 061 P<0. 001 was identified as a protect risk factor of sarcopenia for advanced NSCLC patients. Conclusion The serum Cr/ CysC ratio was significantly correlated with skeletal muscle mass and muscle strength and it could be a simple and effective tool of sarcopenia screening for advanced NSCLC patients.