Lung cancer is the leading cause of preventable death globally and is broadly classified into adenocarcinoma and squamous cell carcinoma depending upon cell type. In this study, we carried out mass spectrometry based quantitative proteomic analysis of lung adenocarcinoma and squamous cell carcinoma primary tissue by employing the isobaric tags for relative and absolute quantitation (iTRAQ) approach. Proteomic data was analyzed using SEQUEST search algorithm which resulted in identification of 25,998 peptides corresponding to 4,342 proteins of which 610 proteins were differentially expressed (≥ 2-fold) between adenocarcinoma and squamous cell carcinoma samples. These differentially expressed proteins were further classified by gene ontology for their localizations and biological processes. Pathway analysis of differentially expressed proteins revealed distinct alterations in networks and pathways in both adenocarcinoma and squamous cell carcinoma samples. In this study, we identified a subset of proteins that shows converse expression between lung adenocarcinoma and squamous cell carcinoma samples. Such proteins may serve as signature markers to distinguish between the two subtypes.