PURPOSE: The preoperative prediction of malignant potential in patients with gastric submucosal tumors (SMTs) plays an important role in decisions regarding their surgical management. METHODS: We evaluated the predictors of malignant gastric SMTs in 314 patients with gastric SMTs who underwent surgery in Chonnam National University Hospital. RESULTS: The malignant SMTs were significantly associated with age (odds ratio [OR], 1.067; 95% confidence interval [CI], 1.042 to 1.091; P < 0.0001), presence of central ulceration (OR, 2.690; 95% CI, 1.224 to 5.909; P = 0.014), and tumor size (OR, 1.791; 95% CI, 1.483 to 2.164; P < 0.0001). Receiver operating characteristic curve analysis showed that tumor size was a good predictor of malignant potential. The most relevant predictor of malignant gastric SMT was tumor size with cut-offs of 4.05 and 6.40 cm. CONCLUSION: Our findings indicated that age, central ulceration, and tumor size were significant preoperative predictors of malignant SMTs. We suggest that 4 cm be selected as a threshold value for malignant gastric SMTs. In patients with a gastric SMT larger than 4 cm with ulceration, wide resection of the full thickness of the gastric wall or gastrectomy with adequate margins should be performed because of its malignant potential.