Objective To investigate the expression of CD55 and its implication on prognosis for patients with gastric stromal tumors.Methods Expression of CD55 was detected by immunohistochemistry staining and the correlation between CD55 and clinicopathological features and prognosis were analyzed on 60 cases of primary gastric stromal tumors from January 2010 to October 2012.Results Of the 60 patients with gastric stromal tumors there were 33 males and 27 females.CD55 was mainly located in the cytoplasm of gastric stromal tumors.There was no statistical difference between CD55 expression and patients' gender and age (P ＞ 0.05).Moreover,the expression of CD55 was closely related to tumor size,mitotic counts,2008 NIH classifications,and distant metastasis at the first visit to the hospital (P ＜ 0.05).During a median follow-up of 58.5 (range 23-78) months,14 patients had tumor progression.Log-rank univariate survival analysis showed tumor size,mitotic counts,2008 NIH classifications,radical resection,distant metastasis at the first clinical visit and CD55 expression were related to progression-free survival (P ＜ 0.001).COX multivariate survival analysis showed that tumor size (HR 11.504,95％ CI:1.085-122.011,P =0.043) and CD55 expression (HR 11.819,95％ CI:1.827-76.477,P =0.01) were independent prognostic factors.Conclusions Up-regulated CD55 might play an important role in the development and metastasis of gastric stromal tumors.