OBJECTIVE To investigate the value of the autofluorescence spectrum of dilute gastric juice in the diagnosis of gastric carcinoma. METHODS The autofluorescence spectrum of dilute gastric juice was scanned with RF-5000 spectrophotofluorometer when the excitation wavelength was set to 288 nm and the emission wavelength ranged from 300 nm to 800 nm. RESULTS We enrolled 251 patients with different gastric diseases including 40 cases with gastric carcinoma in our study. There were three characteristic peaks in the autofluorescence spectrum of gastric juice, which appeared in the spectra of both dilute and indilute specimens, but relative fluorescence intensity index (FI) of the peaks changed with concentration. The spectra of dilute gastric juice (1:20) of both benign and malignant gastric diseases had those three peaks. However, the fluorescence intensity index of the first peak (P1FI) at 320-360 nm of patients with gastric carcinoma was higher than that of patients with benign gastric diseases. The diagnosis model for gastric carcinoma was made by CART V2.0 software. The diagnosis standard for gastric carcinoma was P1FI > 38.995. The model's sensitivity and specificity of prior probability were 85.0% and 91.9% respectively. The sensitivity and specificity of posterior probability were 82.5% and 91.9% respectively. When the diagnosis standard was set to P1FI > 24.34, the sensitivity and specificity were 95.0% and 75.8%, respectively. CONCLUSION The autofluorescence spectrum of dilute gastric juice may become an effective means in the diagnosis and screening of gastric carcinoma.