Schwannoma is a type of peripheral nerve sheath tumor derived from Schwann cells. There have been only a few cases of giant lumbar schwannoma with retroperitoneal extension eroding the vertebral body documented. Thus, managing these tumors presents various challenges. This paper reports a case of a 59-year-old woman who experienced lower back radicular pain for a year. A lumbar magnetic resonance imaging revealed the presence of a giant extradural soft tissue tumor measuring 8.6x7.4x9.7 cm, compressing the right L5-S1 neural foramen and extending into the retroperitoneal space while eroding the L5 vertebral body. The patient underwent surgery via a retroperitoneal approach, and the tumor was successfully resected. Histopathological examination confirmed the diagnosis of schwannoma. In conclusion, giant retroperitoneal lumbar schwannomas with bone invasion are rare, and gross total resection is the preferred treatment option, but the size and location of the tumor can make the surgery challenging.