In this study, Ce: 6 LiCl/LaCl 3 with a high 6 Li concentration was developed as a novel thermal neutron scintillator, in which Ce 3+ serves as an activator for the LaCl 3 phase. The Ce: 6 LiCl/LaCl 3 eutectic was grown in a quartz ampoule (inner diameter: 4.0 mm) using the Bridgman–Stockbarger technique. The grown eutectic contained 0.038 mol/cm 3 6 Li, which is greater than that found in commercially available scintillators such as LiCaAlF 6 single crystals and Li glass. The Ce: 6 LiCl/LaCl 3 eutectic has a lamellar eutectic structure and is optically transparent. A 350-nm emission due to Ce 3+ 4f–5d transition was observed. The light yield under neutron irradiation was estimated to be 5.0 times higher than that of Li glass. In this eutectic, the 6 Li ( $n$ , $a)~^{3}\text{H}$ reaction made the 6 LiCl phase to act as the neutron capture phase and LaCl 3 to act as the scintillator phase.