The corrosion behavior of pure and lanthanum doped, sol–gel-derived, mullite ceramics in nitric acid aqueous solutions with various concentrations was investigated and compared. Samples sintered at a temperature of 1600°C for 4 h were characterized using powder X-ray diffraction, SEM, and energy dispersive X-ray spectroscopy. The corrosion behavior was explored by measuring the amount of eluted ions using atomic absorption spectrophotometry and inductively coupled plasma optical emission spectrometry (ICP-OES). The doped sample was found to be more susceptible to dissolution in the corrodent, having higher leaching rates. The amounts of eluted lanthanum ions were in order of magnitude higher than amounts of silicon and aluminum. Those phenomena were attributed to the incorporation of lanthanum in the glassy phase, forming SiO2–La2O3-rich glassy phase, which can dissolve in corrodent more easily than SiO2-rich glassy phase in the pure sample.