Abstract: The high-temperature interaction of nanostructured Lu₂Si₂O₇ environmental barrier coatings (EBCs) with calcium–magnesium–aluminosilicate (CMAS) was investigated at 1400°C for 1, 10, 25, and 50 h to evaluate the coating’s resistance to CMAS corrosion. The results indicate a phase transformation over time, transitioning from Ca₂Lu₈(SiO₄)₆O₂ apatite and Lu₂Si₂O₇ to solely Lu₂Si₂O₇. The interaction of the Lu₂Si₂O₇ coating with the CMAS melts was divided into three stages based on the corrosion reaction behavior. The delamination cracks were distributed throughout the interface between the Si bond layer and Lu₂Si₂O₇ layer after corroded at 1400°C for 50 h, signifying coating failure. In addition, the influence of monosilicates, disilicates, and corrosion duration on the recession layer thickness was analyzed by comparing previous reports on RE₂SiO₅/RE₂Si₂O₇ coatings (RE = Gd, Yb, Lu, Er). Furthermore, the variation in the thermally grown oxide layer thickness in CMAS-corroded Lu₂Si₂O₇ coatings was systematically investigated.