Objectives <p>We aimed to evaluate the reliability and reproducibility of magnetic resonance imaging (MRI) in the evaluation of epiphyseal invasion (EI).</p> Methods <p>We included paediatric patients with open epiphyseal plates diagnosed with high-grade osteosarcoma (OS) located in the diaphysis or metaphysis of the long bones. Patients underwent neoadjuvant chemotherapy and MRI, including T1-weighted and short tau inversion recovery (STIR)-/T2-weighted sequences. Significant tumour penetration through the growth plate into the epiphysis, high signal intensity in the epiphysis, oedema-like signals in the epiphysis, and growth plate discontinuity were assessed on MRI. Standardised uptake value (SUV) of the lesions and necrosis rate were included in analysis. Histopathological analysis was performed to confirm EI status.</p> Results <p>Thirty-three patients (18 males and 15 females; 4–15 years old; mean age 10.7 years) were included. EI was present in 16 cases. Significant tumour penetration through the growth plate (<i>p</i> = 0.002–0.005), high signal intensity in the epiphysis (<i>p</i> &lt; 0.001–0.005), and discontinuous growth plates (<i>p</i> = 0.002–0.010) were associated with EI, but the latter two showed moderate reproducibility. The association between oedema signals and EI status lacked statistical significance (<i>p</i> = 0.175–0.225), with low specificity and reproducibility. Pre-chemotherapy SUV correlated with EI (<i>p</i> = 0.006). Huvos grade III/IV was associated with a lower incidence of EI (<i>p</i> = 0.02).</p> Conclusions <p>Significant tumour invasion through the growth plate, high signal intensity in the epiphysis, and growth plate discontinuity are reliable indicators of EI on MRI. Oedema-like signals in the epiphysis alone are not associated with tumour invasion.</p>