Abstract： Objective To explore the diagnostic value of k ras mutation detection of specimen obtained by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA)for pancreatic cancer.Methods Seventy-eight patients with pancreatic carcinoma and 49 patients with pancreatic benign diseases were collected from January 2013 to December 2015.All the patients underwent EUS-FNA and cell or tissue samples were collected.DNA was extracted from the samples,and the codon 12 and 13 mutation of K-ras gene was detected by specific nano capture probe.Liquid cytology was also conducted.The sensitivity and specificity of the two methods were compared.Results The K-ras mutation rate was 92.3％ (72/78) in 78 patients with pancreatic carcinoma,which was obviously higher than the mutation rate of 20.4％ (10/49) in 49 patients with pancreatic benign tumors,and the difference was statistically significant (x2 =68.002,P =0.000).The sensitivity of the cytology examination of EUS-FNA specimens in the diagnosis of pancreatic carcinoma was 75.6％,the specificity was 87.8％,Youden index was 0.634,the positive and negative predictive value was 6.196 and 0.227.The detection of K-ras mutations had a sensitivity of 92.3％ and a specificity of 79.6％ in the diagnosis of pancreatic carcinoma,the Youden index was 0.719,the positive and negative predictive value was 4.524 and 0.096.K-ras mutation detection had a higher sensitivity compared with cytology,and the difference was statistically significant (x2 =8.47,P =0.004).The sensitivity was 94.9％ and specificity of 95.9％ using the combination of K-ras mutations and cytology for diagnosing pancreatic cancer,and the specificity was obviously increased compared with only k ras mutation detection and the difference was statistically significant (x2 =6.13,P =0.013).Conclusions K-ras mutation detection of EUS-FNA specimen using nano capture probe system can significantly improve the sensitivity of diagnosing pancreatic cancer,and the sensitivity and specificity could be further improved when combined with cytology.