Platinum-based adjuvant chemotherapy after complete resection has become a standard treatment for patients with stage II to IIIA non-small cell lung cancer; however, not all patients exhibit survival benefits. Therefore, the development of predictive biomarkers for selecting a subgroup of patients who may show improved survival after these treatments is important. Among the 42 proteins identified here using a proteomics analysis that were recognized by autoantibodies in pretreated sera from patients with lung adenocarcinoma who received platinum-based adjuvant chemotherapy, the tumor necrosis factor-receptor-associated protein 1 (TRAP1) was detected in patients with a short disease-free survival. TRAP1 expression was immunohistochemically analyzed in 64 patients with completely resected stage II and IIIA lung adenocarcinoma treated with platinum-based adjuvant chemotherapy. TRAP1 expression was significantly associated with higher p-TNM stage (P = 0.005) and lymph node metastasis (P = 0.017). Moreover, TRAP1 expression was significantly correlated with a shorter disease-free survival (P = 0.028). Furthermore, TRAP1-siRNA-treated LC-2/ad cells derived from lung adenocarcinoma exhibited significantly reduced proliferation and increased sensitivity to cisplatin. These results suggest that TRAP1 expression is a valuable biomarker for predicting the poor survival of platinum-based adjuvant chemotherapy in patients with resected lung adenocarcinoma.