A delay in the union of bone regenerate in surgical lengthening procedures and the healing index (HI) are major factors in the quality of the results in progressive bone lengthening. Early removal of the external fixator (EF) is associated with a low rate of postoperative complications, including pin track infection, and with better muscle and joint function recovery. Addition of intramedullary wires (IMWs) to the EF led to a 9–49% decrease in the HI depending on the clinical series. We hypothesized that IMWs may accelerate the ossification process of bone regenerate and tested it in this experimental study. Methods Progressive tibial lengthening of 28 mm was obtained in 12 dogs operated with the classical Ilizarov technique (group I) and in 12 dogs operated with the same technique and addition of two IMWs 1.5 mm in diameter (group II). The following criteria were assessed: HI, X-ray measurements, and histological aspect of the bone regenerate and postoperative complications. Results The mean HI was 32.3% lower in group II than in group I. The radiological bone union criteria were observed on day 15 of the fixation period in group II versus day 30 in group I. Histology showed that maturation occurred earlier and bone cortices were thicker in group II than group I. Intramedullary ossification was present along the IMW in group II, whereas it was absent in group I. No clinical complications were observed in either group. Discussion The presence of the IMWs clearly contributes to stimulation of the ossification processes of the bone regenerate and to acceleration of bone union. IMWs allowed an earlier removal of the external fixator for a 32% time reduction compared to cases without IMWs. In addition, new intramedullary bone formation and presence of IMWs are expected to increase the mechanical resistance of the bone regenerate. Conclusion Improvement of quantitative and qualitative criteria of bone regenerate in progressive bone lengthening with an EF combined with IMWs was demonstrated in this experimental study. Significance Favorable results encourage the authors to continue using IMWs in addition to the EF in patients treated with long-bone progressive lengthening.