The measurement of impedance is a noninvasive and simple quantitative technique for evaluation of fracture healing. Fractures of the distal radius are the most common long bone fractures, accounting for approximately 20% to 25% of all acute fractures. External fixators have been applied clinically to treat unstable distal radius fractures. The evaluation of radiological findings and clinical signs are current standard methods and are effective in assessing fracture union of the distal radius, but these methods are dependent on subjective elements. For the objective methods, previous studies have shown that measurement of bone mineral density, ultrasound, quantitative computed tomography, and acoustic emission are useful in evaluating bone union. However, due to the complexity and high radiation dose associated with these methods, are seldom used clinically. This study was undertaken to examine the correlation between bone union and impedance at the site of digital radius fractures treated with an external fixator, using an alternating current electrical stimulator and a digital oscilloscope.