We have studied the structure and polytypic defect formation in the 12R perovskite-type Ba4NdMn3O12 compound. Its structure was characterized using transmission electron microscopy (TEM). Like in the 12R ordered oxides of Ba4CeMn3O12 and Ba4PrMn3O12 (Fuentes et al., J. Solid State Chem. 177 ( 2004) 714), a cationic ordering between Nd and Mn is also expected to be established in Ba4NdMn3O12 with the Nd ions located in the corner-sharing octahedra and the Mn ions located in the face-sharing octahedra. We also observed in the Ba4NdMn3O12 phase two types of polytypic faults, i.e., the extrinsic hexagonal-type fault with the stacking sequence ...cch (h) under bar hcc... and the extrinsic cubic-type fault with the stacking sequence ...hhc (c) under bar chh....