Efficacy of tyrosine kinase inhibitor (TKI) therapy depends on epidermal growth factor receptor (EGFR) mutation status in patients with non-small cell lung cancer (NSCLC). There has been an increasing interest in studying mutation-specific rabbit monoclonal antibodies of delE746-A750 mutation in exon 19 and L858R point mutation in exon 21 for detecting EGFR mutants. These two mutations account for approximately 90% of all EGFR mutations. We evaluated the two mutation-specific monoclonal antibodies for the detection of EGFR mutations by immunohistochemistry (IHC) and the relationship with treatment outcome and survival. Twenty-five patients (58.1%) harbored EGFR mutations. These mutations include delE746-A750 mutation for seven patients, L858R point mutation for in eighteen patients. IHC showed, for the delE746-A750 and L858R mutations, sensitivity (57.1% and 66.7%), specificity (97.3% and 100%), positive predictive value (80.0% and 100%), and negative predictive value (94.7% and 80.6%). Analysis for progression-free survival was not correlated to IHC staining, but the overall survival was correlated to IHC staining. These mutation-specific antibodies for delE746-A750 and L858R mutations have high positive predictive value and specificity for predefined EGFR mutations and may be suitable for screening for these predefined mutations. However, negative IHC results required further mutation analyses before excluding EGFR TKI therapy.