Nodular fasciitis is a benign, proliferative lesion of myofibroblasts developed from the fascia. It arises commonly in the upper extremities of adults and in the head and neck region of infants and children. Involvement of the knee is exceedingly rare. We report a case of a 4-year-old girl with a knee mass, causing limitation of knee flexion and pain. Arthroscopic examination was performed followed by arthrotomy and tumor excision. Pathologic findings revealed clusters of spindle cells with arrangement of storiform pattern in a loosely textured mucoid matrix. To the best of our knowledge, this is the youngest patient associated with articular nodular fasciitis in the knee joint.