〔Abstract〕 Objective To investigate the clinical features and prognostic factors of gastric cancer patients under the age of 40. Methods The clinical data of 126 young gastric cancer patients under the age of 40 were retrospectively analyzed.Log-Rank test and Cox regression model were used to analyze prognostic risk factors, respectively. Results The average age of gastric cancer patients in our group was 33.6 years, and there were more female patients than male patients(female ∶male=1.25 ∶1),Upper abdominal pain and fullness discomfort were the most common clinical manifestations, and the predominant sites were gastric antrum angle(43.7%) and gastric body(42.9%).Lauren type was mainly diffuse type(89.7%),Nakamura type was mainly undifferentiated type(91.3%),and WHO type was the most common type of low-adherence carcinoma(46.8%).71.4% of patients were diagnosed with advanced tumor.The most common site of metastasis was the peritoneum.The 1-year and 3-year survival rates were 67.3% and 46.7%, respectively. The results of univariate analysis showed that the levels of serum CA199,tumor length, depth of tumor invasion, lymphatic metastasis, vascular invasion, and surgical approach were risk factors affecting the prognosis of patients.Multivariate analysis revealed that the levels of serum CA199,the depth of tumor invasion and surgical approach were independent prognostic factors. Conclusion Young gastric cancer has a high degree of malignancy and strong biological invasiveness.Most patients are diagnosed at the advanced stage of the tumor, and the overall prognosis is poor.The levels of serum CA199,the depth of tumor invasion and surgical approach were independent prognostic factors.