We have performed electron spin resonance (ESR) measurements on single crystals of a new Mn layered oxide Rb4Mn(MoO4) 3. The Mn2+ ions with S = 5/2 form an equilateral triangular-lattice. The magnetization process of this compound is well reproduced by a theoretical calculation in terms of an Ising-like Heisenberg antiferromagnet on a triangular-lattice. The frequency dependence of the ESR resonance fields along the easy-axis in the low-temperature phase is well explained by the calculations expected from the Ising-like Heisenberg model. We have evaluated the anisotropy and exchange interaction constants, and confirmed that this compound is a good example of the Ising-like Heisenberg antiferromagnet on the regular triangular-lattice.