Osteosarcoma is a form of bone cancer that can originate in any bone throughout the body, although it is most commonly detected in the long bones of the arms and legs. Chondroblastic osteosarcoma, a rare variation of osteosarcoma, is associated with a greater likelihood of recurrence and metastasis. The term "chondroblastic" indicates that certain portions of the tumor have undergone changes, resembling a connective tissue called cartilage. In this report, we present an exceptional case of osteosarcoma affecting the patella. A 54-year-old patient sought consultation at our outpatient clinic, reporting a 10-year history of swelling in the left leg. Magnetic resonance imaging revealed the presence of a large, diverse mass lesion located near the proximal region of the left leg. A Tru-cut biopsy confirmed the presence of chondroblastic osteosarcoma.