Two conflicting ground states, i.e., an antiferromagnetic ground state at 3.8K and aferromagnetic ground state at 5.1 K, have been reported for CePtGe2, which has two nonequivalent crystallographic Ce sites. In this study, we have prepared polycrystalline and single-crystalline CePtGe2 samples and measured their magnetization, specific heat, resistivity, and Seebeck coefficient. The observed bend in resistivity, peak in magnetic susceptibility, and lambda-type anomaly in specific heat at T-N = 3.8K and the metamagnetic transition in this CePtGe2 suggest antiferromagnetism at low temperatures. No evidence of ferromagnetic order was found in the studied temperature range, indicating possible crystal polymorphism with ferromagnetic character. The large susceptibility around TN and the Schottky-type specific heat indicate a well-localized f -electron state. However, the large residual gamma and X(0) indicate an itinerant heavy f -electron state. These findings suggest the coexistence of localized and heavy itinerant states corresponding to f electrons at the two Ce sites in this antiferromagnetic CePtGe2. The field dependence of magnetization indicates a sudden increase in magnetization at weak magnetic fields (similar to 0.2T), followed by a plateau at fields above 0.2 T, resulting in a possible different polarized metamagnetic state via interaction between localized and itinerant f electrons.