In the treatment of posttraumatic valgus deformity of the pediatric little finger, it is usually difficult to achieve accurate correction of angular and rotational deformity using closing wedge osteotomy. We report two cases of valgus deformity of the little finger (both 11-year-old female patients) successfully treated using opening wedge osteotomy followed by intramedullary semirigid fixation with a single Kirschner wire. A wire tip inserted from the retrocondylar fossa of the proximal phalangeal head was advanced along the radial side of the intramedullary cortex after gradual opening of the osteotomy site. If needed, further fine adjustment of the rotational alignment can be performed even after K-wire insertion. Postoperatively, the gap between the little and ring fingers in the fully extended and adducted position and the finger overlapping in the fully flexed position were completely resolved. The flexibility of the pediatric bone and sagittal clearance between the wire and the inner wall of the proximal phalangeal medullary cavity allow fine adjustment of the rotational alignment even after wire insertion.