Abstract: Objective To detect the expression of aldehyde dehydrogenase 1A1（ALDH1A1） in gastric cancer tissues and clinical significance. Methods ALDH1A1 expression in 1072 gastric cancer tissues and paracacinoma tissues was detected by immunohistochemistry. The associations of ALDH1A1 with clinicopathological characteristics and overall survival（OS） were subsequently assessed. Results The positive expression rates of ALDH1A1 in gastric cancer tissues and para-cacinoma tissues were 49.9％（535／1072）and 43.3％（465／1072），with statistic significance（P＜0.05）.The expression of ALDH1A1 was associated with age， depth of gastic wall invasion， differentiation， lymph node metastasis and TNM stage（P＜0.05）. The median OS of 1072 patients was 32.2 months， and for the patients with positive expression and negative expression of ALDH1A1 were 23.3 and 60.4months（P＜0.001）. Cox multivariate regression model revealed that ALDH1A1 expression， differentiation, TNM stage, age， lymph node metastasis， tumor thrombus, depth of gastic wall invasion and nervous invasion were independent factors influencing OS.Conclusion ALDH1A1 is obviously upregulated in gastric cancer tissues， and correlated with poor prognosis， which may become a new tumor maker for predicting prognosis of gastric cancer.