Background Emerging reports demonstrated that PIWI-interacting RNAs (piRNAs) played an indispensable role in tumorigenesis. However, it still remains elusive whether piR-1245 in gastric juice specific in stomach could be employed as a biomarker for gastric cancer (GC). The present work is aiming at exploring the possibility of piR-1245 in gastric juice as a potential marker to judge for diagnosis and prognosis of gastric cancer. Methods Gastric juice was collected from 66 GC patients and 66 healthy individuals. Quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR) was employed to measure the levels of piR-1245 expression. Then, the pattern of piR-1245 expression in gastric juice was determined between GC patients and healthy individuals. A receiver operating characteristic (ROC) curve was constructed for distinguishing GC from healthy individuals. Results Gastric juice piR-1245 levels in GC were higher than those of controls (P < .0001). The value of area under ROC (AUC) was 0.885 (sensitivity, 90.9%; specificity, 74.2%; 95% confidence interval, 0.8286 to 0.9414). High gastric juice piR-1245 expression was signally correlated with tumor size (P = .013) and TNM stage (P = .001). GC patients with high piR-1245 expression in gastric juice exerted a poorer overall survival (OS) (P = .0152) and progression-free survival (PFS) (P = .013). COX regression analysis verified that gastric juice piR-1245 expression was an independent prognostic risk variable for OS (P < .05). Conclusions The current study suggested that piR-1245 in gastric juice had the potential to be a useful biomarker for GC detection and prognosis prediction.