Abstract: Objective: This study tried to investigate the effect or serum CYERA21-1 as a new lung cancer marker in clinical diagnosis and monitoring the prognosis of non small cell lung cancer (NSCLC), especially in squamous cell cancer (SQC).Methods: The values of serum CYERA21-1 and CEA (Carcinoembryonic antigen) were determined in 92 patients with lung cancer (64 cases) and benigh lung diseses (28 cases) admitted in our hospital from August 1996 to April 1997, and compared the deference values of serum CYERA21-1 between different histological types, clinical stages before and after therapy of lung cancer. Results: The positive rates of serum CYERA21-1 and CEA in lung cancer were 42.19% and 34.53% respectively significantly higher than in benign lung diseses; the values or positive rates of serum CYERA21-1 in SQC were higher significantly than adenocarcinoma (P＜0.01), higher in stage Ⅳ than stage Ⅲ of SQC (P＜0.05), decreaed after treatment in NSCLC. Conclusion: The serum CYERA21-1 is a useful diagnotic and monitoring tumor marker in lung cancer particulaely for squamour cell lung cancer.