Venous aneurysms are rare vascular malformations that can lead to significant clinical complications, including thrombosis, pulmonary embolism, rupture, and even fatal outcomes when not promptly and adequately managed. This case report presents a liver transplant patient under immunosuppressive therapy who developed a rapidly progressing great saphenous vein aneurysm, ultimately requiring urgent surgical intervention due to acute bleeding from the ruptured aneurysm. Immunosuppression emerges as a potential key factor in the formation and rapid growth of the aneurysm, with the pathophysiological mechanism potentially involving increased expression of specific matrix metalloproteinases. Further research is warranted to gain a better understanding of the role of immunosuppression in the development of venous aneurysms.