Purpose: Our aim was to comparatively investigate the strain ratio and thickness of the Achilles tendon in children with cerebral palsy (CP), and to elucidate whether there is a correlation between biomechanical features of the Achilles tendon and strain ratio. Methods: A total of 155 participants (72 CP patients and 83 healthy controls) who underwent real-time elastography of both Achilles tendons were studied. A linear transducer (4.8–11.0 MHz) was used to obtain the images. Correlation analysis between age, length, and thickness of the Achilles tendon, and strain ratio (SR) was performed by means of Pearson correlation and Spearman’s rho tests. Results: Comparison of results obtained from CP patients and controls showed that the length of the Achilles tendon was shorter (p < 0.001) and SR was higher (p < 0.001) in CP patients. In CP patients, there was a positive correlation between SR and age and between SR and the thickness and length of the Achilles tendon (p < 0.001 for all). Furthermore, the length of the tendon and age were positively associated (p < 0.001). ROC analysis revealed that the cut-off value for SR was 1.89. Conclusion: The results of the present study demonstrated that real-time elastography can constitute a simple, practical, and noninvasive method for evaluation of the elasticity of the Achilles tendon in children with CP.