Hot corrosion is one of the significant failure mechanisms in hot-section components, especially when molten CaO–MgO–Al2O3–SiO2 (CMAS) deposits attack the thermal barrier coating and facilitate its degradation at elevated temperatures. This work concentrates on the hot corrosion behavior of LaMgAl11O19 ceramic as a promising candidate for TBCs after exposure to CMAS at 1250 °C for 1–16 h in air. The phase constituents and morphologies of the hot corrosion products were investigated by X-ray diffraction and scanning electron microscopy, respectively. Energy-dispersive X-ray spectroscopy was employed for elemental and microstructure analysis. The corrosion products are identified to be CaAl2Si2O8 and Ca(Mg,Al)(Al,Si)2O6 due to the interaction between LaMgAl11O19 ceramic and melt-CMAS by dissolution-reprecipitation. The hot corrosion mechanism was further proposed based on the phase diagram.