Extracellular signal-regulated kinases (ERKs), Akt, and signal transducer and activator of transcription 3 (STAT3) are on signal transduction pathways triggered by epidermal growth factor receptor (EGFR). The purpose of this study was to evaluate the expressions of these peptides and to correlate the level of EGFR expression with downstream-activated peptide expression in non-small-cell lung cancer (NSCLC). A total of 60 specimens were studied by immunohistochemistry. EGFR overexpression was detected in 78% of specimens, but no significant relationship was found between it and any clinicopathological factors investigated. Phosphorylated (p)-ERK, p-Akt, and p-STAT3 expressions were observed in 28, 53, and 58% of specimens, respectively, and p-Akt and p-STAT3 expressions were correlated with well-differentiated tumor (P=0.045 and 0.014, respectively). Half of the 60 specimens expressed two or three downstream-activated peptides. The level of EGFR expression was associated with expressions of p-ERK and p-Akt (P=0.045 and 0.020, respectively). In a preliminary analysis, no peptides examined had an impact on relapse-free survival. In summary, various signal transduction pathways appeared frequently to participate in NSCLC, and the level of EGFR expression appeared to correlate with those of activated ERK and Akt, suggesting some role of receptor overexpression in more potent downstream activation.