Background: Some presumed resectable pancreatic cancer patients harbor radiographically occult metastases that are incidentally identified at the time of abdominal exploration. This study aims to identify novel diagnostic or predictive microRNA (miRNA) markers for subclinical peritoneal dissemination in patients with pancreatic cancer undergoing abdominal exploration. Methods: Peritoneal lavage fluid samples were harvested from 74 patients with pancreatic cancer at the time of staging laparoscopy. Microarray analysis was performed using peritoneal lavage fluids with positive and negative cytology. Candidate microRNA expression was quantified and validated by droplet-digital PCR assays. Results: In the miRNA array analysis, miR-593-3p showed significant upregulation in peritoneal lavage fluids with positive cytology. Of the 74 patients validated, peritoneal lavage fluids with positive cytology had significantly higher expression of miR-593-3p than those with negative cytology (P < 0.001). Even in cases with no peritoneal dissemination and negative cytology, multivariate analysis revealed that elevated miR-593-3p expression was significantly correlated with worse overall survival than those with low expression (hazard ratio: 3.474, P = 0.042). Of the 48 patients who underwent pancreatectomy, multivariate analysis also demonstrated that higher expression of miR-593-3p in peritoneal lavage was the only significant poor prognostic marker influencing both overall survival (hazard ratio: 23.38, P = 0.005) and recurrence-free survival (hazard ratio: 5.700, P = 0.002). Conclusions: Elevated miR-593-3p expression in peritoneal lavage suggests the presence of subclinical micrometastasis even in cases with localized pancreatic cancer, and miR-593-3p could be a useful prognostic predictor for pancreatic cancer patients undergoing staging laparoscopy.