La_1-zNd_z(Fe_0.88Si_0.12)₁₃ and their hydrides were investigated to obtain large magnetocaloric effects (MCEs) in a wide temperature range, including room temperature, for applications in magnetic refrigents. Since the magnetization change due to the itinerant-electron metamagentic (IEM) transition for La_1-zNd_z(Fe_0.88Si_0.12)₁₃ becomes larger with increasing z, the isothermal magnetic entropy change ΔS_m and the relative cooling power (RCP) are enhanced. In addition, the Curie temperatrue T_C of La_0.8Nd_0.2(Fe_0.88Si_0.12)₁₃  is increased from 193 to 319 K by hydrogen absorption, with the IEM transition. The maximum value of -ΔS_m, -ΔS_m ^max, in a magnetic field change of 2 T for La_0.8Nd_0.2(Fe_0.88Si_0.12)₁₃H_1.1 is about 23 J/kg K at T_C = 288 K, which is larger than that of 19 J/ kg K at T_C = 276 K for La((Fe_0.88Si_0.12)₁₃H_1.0. The value of RCP = 179 J/kg of the former is also larger than 160 J/ kg of the latter. It is concluded that the partial substitution of Nd improves MCEs in a wide temperautre range, including room temperature.