Pancreatic cancer is an aggressive malignancy with a poor prognosis. Single-nucleotide mutations in the KRAS gene are detected in the majority of patients with pancreatic ductal adenocarcinoma (PDAC), the most common type of pancreatic cancer. Identifying KRAS mutations by liquid biopsy could be effective for detecting de novo and recurrent PDAC; however, sensitive and accurate detection remains challenging. We examined the utility of oligoribonucleotide interference-PCR (ORNi-PCR) followed by real-time PCR or droplet digital PCR (ddPCR) for detecting KRAS single-nucleotide mutations by liquid biopsy. A model of cell-free DNA was used to demonstrate that the ORNi-PCR-based methods are more sensitive and accurate for detecting KRAS mutant DNA than conventional real-time PCR or ddPCR. ORNi-PCR-based methods could be useful for early detection of de novo and recurrent PDAC by liquid biopsy for cancer diagnosis.