The preparation, complex magnetic properties and room-temperature magnetocaloric effect in Nd(Cu3-xMnx)Mn4O12 with cation distribution (Nd3+)A(Cu3-x2+xMnx3+)A'(Mn1+x3+Mn3-x4+)BO122- (x = 1 and 1.5) have been reported. Both compounds show a sharp paramagnetic-ferromagnetic (FM) transition at TC of 300 and 280 K, respectively. The substitution of Cu by Mn at the A' site induces the emergence of a spin glass state below ≈63 K for x = 1 and ≈72 K for x = 1.5 compound. Another antiferromagnetic-like magnetic transition is also observed in both compounds at 23 and 28 K, respectively, which is discussed as the antiferromagnetic coupling between Nd3+ at the A' site and (Mn3+/Mn4+) at the B site. These two compounds exhibit room-temperature magnetocaloric effect. For a small field of 2 T, the maximum magnetic entropy changes -ΔSM are 1.5 J/kg K at 300 K and 1.4 J/kg K at 280 K, respectively. Moreover, the -ΔSM(T) curves show an asymmetric distribution, resulting in high refrigerant capacity values for both compounds. We further demonstrate the distinct roles of the A'- and B-site spins on the magnetic properties and the origin of the spin-glass-like state in double distorted perovskites Ln(Cu3-xMnx)Mn4O12 family of compounds.