Abstract: Objective To investigate the relationship between expressions of thyroid transcription factor 1（TTF-1） and epidermal growth factor receptor（EGFR）， and EGFR mutations of 19 and 21 exons in lung adenocarcinomas. Methods For 153 cases of lung adenocarcinomas obtained by surgical resection and puncture biopsy，immunohistochemistry was used to detect the expression of TTF-1 and EGFR， and amplification refractory mutation system was used to detect mutations of EGFR 19 and 2l exons. Furthermore， the relationship between expressions of TTF-1 and EGFR， and EGFR mutations of 19 and 21 exons were also investigated. Results Sixty-eight cases of EGFR gene mutations were found， including 32 cases in 19 exons and 36 cases in 21 exons. Among 153 cases of lung adenocarcinomas， 50.0％（24／48）， 62.5％（25／40） and 83.1（54／65） of EGFR expression（+++） and 25.0％（12／48）， 37.5（15／40）， 63.08％（41／65） of EGFR mutations were found in 48， 40 and 65 cases of TTF-1 expression（0-+）、（++） and（+++）， respectively. Besides， 16.7％（3／18）， 34.4％（11／32） and 52.4％（54／103） of EGFR mutations were found in 18， 32， 103 cases of EGFR expression of（0-+），（++），（+++）. It was observed that the ratios of EGFR expression（+++） and EGFR mutations also increased with the increased expression of TTF-1. It was also found that the EGFR mutations increased correspondingly with the increased EGFR expression. The correlations of TTF-1 expression and EGFR expression， TTF-1 expression and EGFR mutations， EGFR expression and EGFR mutations were statistically significant with the corresponding r of 0.940， 0.916， and 1.000， respectively. Conclusion Expressions of TTF-1 and EGFR and EGFR mutations of 19 and 21 exons are relevant to each other in lung adenocarcinomas. Detection of TTF-1 expression can be used to preselect the EGFR mutations for target therapy. Clinical doctors can predict EGFR mutations to guide the timely and effective clinical diagnosis and treatment by combined evaluating the expression of TTF-1 and EGFR when it is urgent for chemotherapy or target therapy but hard to undertake the detection of EGFR gene mutation in some areas.