FeBO₃ and Fe₃BO₆ are antiferromagnets with T_N ≈ 348 K and 508 K respectively. This work presents the results of the study of the thermal expansion and phase transitions occurring in these borates by hightemperature X-ray powder diffraction and Mössbauer spectroscopy in a wide temperature range. Unit cell parameters are refined by the Rietveld method at different temperatures. For both compounds an abrupt change in thermal expansion coefficients α is revealed near the magnetic antiferromagnet–paramagnet phase transition.