A previously unreported triangular lattice (TL) antiferromagnet, TmZnGaO4, was synthesized as single crystals, and its crystal structure, magnetic susceptibilities, and specific heat were reported. Its crystal structure is isomorphic to that of the transverse-field Ising antiferromagnet TmMgGaO4, with Tm3+ ions located in the TLs, separated by a nonmagnetic bilayer composed mainly of Ga3+ and Zn2+ ions. The magnetic susceptibilities indicate the dominating antiferromagnetic interactions. The magnetization curves (M–H) exhibit strong easy-c-axis anisotropy, with a clear one-third magnetic plateau emerging, consistent with a field-induced up–up–down (↑↑↓) spin configuration. Instead of forming a conventional long-range magnetic order, the system exhibits two broad humps at 0.11 K and 2.81 K in zero-field specific heat measurements, revealing dominant strong spin fluctuations and pointing to potential relevance to BKT physics. The above results reveal its future interest in exploring exotic quantum spin states in TmZnGaO4.