Background & Aims This study assessed the prognostic value of LCR in patients with cancer-associated malnutrition (CAM). Systemic inflammatory markers, particularly the lymphocyte-to-C-reactive protein ratio (LCR), are related to the survival of patients with CAM. The present retrospective analysis based on a prospective multicenter cohort study, which involved 1,437 hospitalized patients with CAM. Methods The area under the receiver operating characteristic curve (AUC) of ten inflammatory indicators — LCR, advanced lung cancer inflammation index, neutrophil-to-lymphocyte ratio, prognostic nutritional index, modified Glasgow prognostic score, systemic immune-inflammation index, albumin-to-globulin ratio, LCR score, glucose-to-lymphocyte ratio, and platelet-to-lymphocyte ratio—were constructed. Nutritional status, blood markers, and quality of life (QoL) were evaluated within 48 h of admission. The overall survival (OS) was evaluated from September 1 to December 29, 2021. Results A total of 1,431 cancer patients diagnosed with malnutrition based on the Global Leadership Initiative on Malnutrition (GLIM) criteria. Male patients were 62.8% of all, and the mean age was 60.66 years old. The AUC of LCR was higher than that of other inflammatory markers. The restricted cubic spline (RCS) of the Hazard ratios (HRs) showed an inverse L-shaped relationship with LCR. In addition, patients with low LCR had significantly poorer OS than those with high LCR. The addition of LCR to the model increased the predictive ability of 1-year mortality (AUC increase of 0.036), 3-year mortality (AUC increase of 0.038), and 5-year mortality (AUC increase of 0.031). Conclusions Assessing the LCR can help the medical staff identify cancer patients with nutritional deficiency at high risk of oncological outcomes and develop individualized therapeutic strategies.