BACKGROUND/AIMS: To minimize injury, less invasive surgery including laparascopic surgery and endoscopic mucosal resection are increasingly used for the treatment of gastric cancer nowadays. Therefore, accurate preoperative staging is important to decide adequate treatment modality. Endoscopic ultrasonography (EUS) is reported to be an accurate diagnostic modality to evaluate the depth of tumor invasion. Especially, evaluation of T-2 stage is important to determine operation. We tried to reveal the factors affecting the accuracy of EUS for the evaluation of T-2 stage gastric cancer. METHODS: Among 367 patients who underwent EUS to evaluate preoperative stage, we compared EUS findings and histopathological findings retrospectively. RESULTS: A total of 270 patients were diagnosed as early gastric cancer, and 97 patients as advanced gastric cancer. The overall concordance rate was 78.2% (287/367), over-estimation rate 14.2% (52/367), and under-estimation rate 7.6% (28/367). Among T-2 stage cancer, over-estimation rate was 27.0% (20/74), and under-estimation rate 21.6% (16/74). These were relatively high compared with those with over-estimation. Among T1 lesions, 20.6% (22/107) were over-estimated as the invasion into proper muscle layer. Compared with sm1 lesion (17.9%), sm3 lesions showed higher over-estimateion rate (25.7%). In the presence of submucosal fibrosis, sm1 lesions were over-estimated as T-2 lesion. Sm2 and sm3 lesions were not related to submucosal fibrosis. Factors affecting over-estimation as T-2 lesions were the size of tumor, the presence of submucosal fibrosis and connective tissue hyperplasia, and ulcer (p<0.05). Microscopic invasion did not affect the accuracy of EUS findings. CONCLUSIONS: In T-2 gastric cancer, the presence of submucosal fibrosis, tumor size, and ulcer were the affecting factors for the over-estimation of the depth of invasion using EUS in gastric cancer. To improve preoperative diagnostic accuracy in T-2 stage cancer, a new diagnostic improvement in EUS is needed.