Purpose: Serum markers that enable diagnosis in the early stage of lung cancer have not been discovered. We have developed a LC-MRM-MS assay for the identification of potential early marker proteins for lung adenocarcinoma. Experimental design: LC-MRM-MS assay was used for measuring the level of 35 candidate peptides in plasma from 102 lung adenocarcinoma patients (including n=50, 16, 24, and 12 in stage I, II, III, and IV, respectively.) and 84 healthy controls. Stable isotope labeled standard peptides were synthesized to accurately measure the amount of these proteins. Results: Seven proteins were found to be able to distinguish stage I patients from controls. These proteins were combined in to a protein marker panel which improved the sensitivity to discriminate stage I patients from controls and resulted in a high classification performance with cross-validated area under the curve=0.76. Besides, we found that low expression of eukaryotic initiation factor 4A-I and high expression of lumican showed significantly poor prognosis in overall survival (p=0.012 and 0.0074, respectively), which may be used as prognostic biomarkers for lung cancer. Conclusion and clinical relevance: Proteins highlighted here may be used for early detection of lung adenocarcinoma or therapeutics development after validation in a larger cohort.