Objective To study whether plasma amino acid metabolites in patients with gastric cancer can be used as biomarkers for the diagnosis of gastric cancer. Methods The levels of 24 kinds of plasma amino acids were detected by ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS), and were compared between patients with gastric cancer and normal controls, between patients with different stages of gastric cancer, and between gastric cancer patients before and after operation. Results The levels of 18 kinds of plasma amino acids including alanine (Ala), glycine (Gly) and glutamic acid (Glu) in gastric cancer patients were significantly lower than those in the normal controls, while the levels of valine (Val), arginine (Arg) and serine (Ser) were significantly higher than those in the normal controls (all P<0.05); there were no significant differences in symmetric dimethylarginine (SDMA), kynurenine (Kyn) or hippuric acid (HA) levels between the two groups (P>0.05). The plasma level of Arg in patients with Ⅲ-Ⅳ stage of gastric cancer was significantly higher than that in the Ⅰ-Ⅱ stage, while the plasma glutamine (Gln), Glu, methionine (Met) and phenylalanine (Phe) levels were significantly lower than those in the Ⅰ-Ⅱ stage (all P<0.05). The levels of plasma leucine (Leu), Arg and citrulline (Cit) in patients after operation were significantly lower than those before operation, while the plasma Gln, lysine (Lys), Glu and Phe levels were significantly higher than those before operation (all P<0.05). Conclusion Amino acids metabolites in plasma of patients with gastric cancer such as Gln and Arg play important roles in the early prediction of gastric cancer.