Pycnodysostosis is a rare hereditary autosomal recessive disease, characterized by systemic bone sclerosis. Fracture of the femur often resulted in nonunion. Treatment for a non-united fracture of this nature is extremely challenging because of hard sclerotic but brittle bone quality, causing problems in fixation. This report presented a case of bilateral subtrochanteric femur fracture with recalcitrant nonunion at the right femur that was successfully managed by internal fixation and bone grafting with calcium-based demineralized bone matrix (DBM) in a 16-year-old female patient with pycnodysostosis. With the osteoconductive and osteoinductive properties, the use of calcium-based DBM is an alternative treatment for the nonunion of subtrochanteric femoral fractures in patients with pycnodysostosis.