We succeeded in growing a high-quality NpCoGa5 single crystal by the Ga-flux method and measured its electrical resistivity, specific heat, magnetic susceptibility and magnetization. NpCoGa5 is an antiferromagnet with a Neel temperature of 47 K. The magnetic moment of Np is directed along the [001] direction of a tetragonal crystal structure. A sharp metamagnetic transition was observed at H-m = 43 kOe for H || [001], where the antiferromagnetic state is changed to the paramagnetic state above H-m. The ordered moment was determined to be 0.74 mu(B)/Np. The magnetic properties were discussed on the basis of the crystalline electric field scheme of the 5f(4) configuration.