The multiple precipitation behavior of NbC and Cu particles in martensitic structure was investigated by using 0.05C-0.46Nb-2Cu-1.5Mn steel (NbC-Cu steel). Additionally, 0.05C-0.45Nb-2Mn steel (NbC steel) and 2Cu-5Mn steel (Cu steel) were also prepared to examine the respective precipitation behaviors of NbC and Cu. Aging treatment at 873K after quenching revealed that these steels exhibit typical age hardening. Comparing the NbC steel and Cu steel in the precipitation rate, the Cu precipitated much faster than the NbC. On the other hand, the peak hardness in NbC-Cu steel is higher than that by the respective precipitations in NbC steel and Cu steel. Besides, the aging time for the peak hardness in NbC-Cu steel was between those in NbC steel and Cu steel. This suggests that the NbC and Cu particles were separately precipitated within martensite matrix and each of them contributed to the hardening in NbC-Cu steel. As a result of TEM investigation for crystallographic characteristics of the precipitates, the NbC and Cu particles had different crystallographic orientation relationship with tempered martensite matrix: Baker-Nutting relationship for NbC particle and Kurdjumov-Sachs relationship for Cu particle.