Abstract Background: Gastric cancer is one of the most common forms of cancer worldwide. The progression of chronic atrophic gastritis (CAG) is involved in gastric carcinogenesis. With the progression of chronic atrophic gastritis, the risk of gastric cancer increased in a stepwise fashion. Non-invasive tools for early gastric cancer are required to improve the prognosis. MicroRNAs (miRNAs), a class of small non-coding RNAs of 19-22 nucleotides in length, function as post-transcriptional regulators by directly cleaving target messenger RNA or translational repression. MiRNAs in serum have been shown to be potential biomarkers in various type of cancers and several miRNAs have been reported in gastric cancer. The purpose of present study was to identify a serum miRNA expression profile that can serve as a novel diagnostic biomarker for early gastric cancer. Materials and Method: We defined a normal gastric mucosa as grade0, CAG classified C-1, 2 in Kimura-Takemoto classification as grade1, CAG classified C-3, O-1 in Kimura-Takemoto classification as grade2, and CAG classified O-2, 3 in Kimura-Takemoto classification as grade3. We obtained 344 serum samples, which gathered from 19 health people (grade0), 125 patients with chronic atrophic gastritis (grade1: 54, grade2: 36, grade3: 35), and 200 patients with early gastric cancer. The miRNAs were extracted from serums and miRNA microarray analysis was performed. In the discovery phase, we analyzed 71 cases (grade0: 11, grade1: 20, grade2: 20, grade3: 20). Next, in the training phase, we analyzed 73 cases (grade0: 8, grade1: 34, grade2: 16, grade3: 15). Then, we analyzed 200 early gastric cancer serum samples. Result: The microarray analysis identified a profile of miRNA (miRNA-196b-3p) as a biomarker for early gastric cancer. The analysis results showed that the expression level of the serum miRNA was correlated to degree of CAG and carcinogenesis. When compared with grade0,1,2 and grade3, the area under the receiver operating characteristic (ROC) curve of this serum miRNA signature was 0.730 and 0.763 for the two sets of serum samples. There was significant difference in serum value of miRNA-196b-3p between grade1-3 and early gastric cancer (p=0.003). Conclusion: Serum miRNA-196b-3p is good biomarker for early gastric cancer. Citation Format: Atsushi Fujii, Sho Nambara, Yosuke Kuroda, Shuhei Ito, Hidetoshi Eguchi, Takaaki Masuda, Takao Otsuka, Masafumi Nakamura, Koshi Mimori. MicroRNA-196b-3p identified from serum microRNA expression profiling is a potential diagnostic biomarker for gastritis and early gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5395.