Objective Pseudoaneurysm rupture associated with unresected pancreatic cancer can cause rare but fatal hemobilia and gastrointestinal bleeding. This study aimed to identify factors predicting pseudoaneurysm rupture. Methods We conducted a single-center case-control study of unresected pancreatic cancer patients treated at Shizuoka General Hospital between January 2011 and July 2020 using a retrospective cancer registry database. Included in the study were 611 consecutive patients with unresected pancreatic cancer, of whom 55 developed overt upper gastrointestinal bleeding or hemobilia. Twenty patients were excluded, as they had not undergone contrast-enhanced computed tomography (CT) or angiography. Patients were classified into pseudoaneurysm and non-pseudoaneurysm groups. One patient with arterial bleeding but without obvious pseudoaneurysm was included in the pseudoaneurysm group. Factors predicting pseudoaneurysm rupture at the onset of overt gastrointestinal bleeding were investigated using a logistic regression analysis. CT findings revealing air bubbles inside the tumor were described as intratumoral air bubbles. Results Thirty-five patients were included (15 in the pseudoaneurysm group, 20 in the non-pseudoaneurysm group). In the multivariate analysis, intratumoral air bubbles [odds ratio (OR), 12.9; 95% confidence interval (CI), 2.14-77.9; p=0.005] and hematemesis (OR, 6.30; 95% CI, 1.03-38.6; p=0.047) were independent predictors of pseudoaneurysm rupture. In addition, patients who experienced successful hemostasis and were re-administered chemotherapy survived more than six months. Conclusions This study reveals that intratumoral air bubbles and hematemesis may predict pseudoaneurysm rupture at the onset of overt gastrointestinal bleeding. For patients presenting these findings, an examination with conventional or CT angiography may lead to an early diagnosis and improve the patient prognosis.