Crystalline scintillators with an elpasolite structure (A1+2B1+C3+X1−6) have received significant attention owing to their good energy resolution and high light yield. We also focused on Tl-based scintillators, since Tl ion has a large atomic number (Z = 81) and there are some reports on these scintillators which have good scintillation properties. Herein, we developed a new self-activated elpasolite crystalline scintillator, Tl2NaYCl6, with a large effective atomic number (Zeff = 70.2). According to the XRD pattern, Tl2NaYCl6 crystal has a tetragonal structure belonging to the P4/nbm (125) space group and with lattice constants of 1.052 and 1.060 nm. The PL excitation and emission wavelengths are 240 and 390 nm, respectively. The scintillation emission wavelength is 430 nm, which is characteristic of thallium-based self-activated scintillators and suitable for PMTs. These PL and scintillation emissions are similar to other Tl-based scintillators and attributed to self-trapped excitons. The scintillation decay time constants are 350 (80%) and 2.5 × 103 (20%) ns. These decay time constants are also characteristic of thallium-based self-activated scintillators. The light yield is 2.3 × 104 photons/MeV, which is higher than that of Ce-doped Gd2SiO5 (GSO) (1.0 × 104 photons/MeV), a commercial scintillator, and is similar to those of other self-activated elpasolite scintillators, such as Cs2LiCeCl6 (2.2 × 104 photons/MeV) and Tl2LiGdBr6 (~ 2.7 × 104 photons/MeV). The energy resolution of the crystal is 6.3%, which is also better than that of the commercial scintillator, GSO (8.6%), and also similar to those of other self-activated elpasolite scintillators, such as Cs2LiCeCl6 (5.5%) and Tl2LiGdBr6 (7.2%).