In this study, Ce:6LiCl/LaCl3 with a high 6Li concentration was developed as a novel thermal neutron scintillator, in which Ce3+ serves as an activator for the LaCl3 phase. The Ce:6LiCl/LaCl3 eutectic was grown in a quartz ampoule (inner diameter: 4.0 mm) using the Bridgman–Stockbarger technique. The grown eutectic contained 0.038 mol/cm3 6Li, which is greater than that found in commercially available scintillators such as LiCaAlF6 single crystals and Li glass. The Ce:6LiCl/LaCl3 eutectic has a lamellar eutectic structure and is optically transparent. A 350 nm emission due to Ce3+ 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 6Li (n, a) 3H reaction made the 6LiCl phase to act as the neutron capture phase and LaCl3 to act as the scintillator phase.