Magnetic properties and magnetocaloric effect of Ho2PtSi3, a new ternary intermetallic compound with the orthorhombic Ba2LiSi3-type structure, are studied by dc magnetization, ac susceptibility, magnetic relaxation, specific heat, and magnetic memory effect measurements. The experimental results indicate that this system undergoes a magnetic phase transition from a paramagnetic state to a ferromagnetic cluster state at a temperature T-C similar to 6.5 K followed by a cluster glass transition at T-f similar to 5.8 K. The typical cluster glass features observed below Tf for Ho2PtSi3 include (1) broad peak in specific heat curve, (2) frequency dependent cusp in ac susceptibility curve, (3) evident irreversible magnetism, (4) long-time magnetic relaxation behavior, and (5) zero-field-cooling magnetic memory effect. On the other hand, the large values of magnetic entropy change, relative cooling power and adiabatic temperature change are estimated near TC under a field change. These results suggest that Ho2PtSi3 can be classified as a huge ferromagnetic cluster glass system with large magnetocaloric effect.