The phase transition of La-doped [Bi1/2(Na0.82K0.18)1/2]TiO3 (BNKT) ceramics was investigated by using high-temperature X-ray diffraction and temperature-dependent dielectric measurements. Undoped BNKT was found to be a nonergodic relaxor, which was evidenced by the presence of a depolarization temperature below which polar nanoregions were frozen. However, La-doped BNKT ceramics are believed to be composites consisting of ergodic and nonergodic relaxors. The results suggest that a nonergodic relaxor with tetragonal symmetry might be distributed in an ergodic relaxor matrix with pseudocubic symmetry.