Introduction: Operative treatment of mallet finger fractures is generally recommended for patients in whom more than one-third of the articular surface is involved with volar subluxation. We present a case of conservative treatment with chronic nonunion of a mallet finger fracture after failed mallet finger surgery. Presentation of Case: A 16-year-old boy presented with a bony fragment (mallet formation) of his left long finger. The fragment occupied 40% of the articular surface, with volar subluxation of the distal phalanx. Percutaneous needle curettage of the fracture site and pinning were performed. Six weeks later, the fragment was displaced and had rotated. Hence, all the pins were removed, and a splint was applied. The fracture displayed nonunion and volar subluxation of the distal phalanx. The patient continued with the splinting, and the fracture finally healed. At 27 months after the surgery, radiological examination showed very good remodeling of the distal interphalangeal joint surface with anatomic joint congruence. Functional results at 27 months were good according to Crawford's classification. Conclusion: Chronic nonunion of a mallet finger can be cured conservatively even when a fracture gap is seen along with displacement of the fragment and volar subluxation of the distal phalanx.