The NdBaMnFeO6-delta layered perovskite was synthesized by a topotactic reaction in the N-2/H-2 atmosphere for the first time while controlling the sample mass during the experiment. The X-ray powder diffraction (XRPD) patterns of the samples with different oxygen content refined by the Rietveld method revealed the YBaCuFeO5-type tetragonal structure of NdBaMnFeO6-delta (sp. gr. P4/mmm). The results obtained by selected area electron diffraction (SAED) and by high-resolution transmission electron microscopy (HRTEM) clearly evidenced the doubling of the c parameter without any additional superstructure reflections. The NdBaMnFeO6-delta phase exhibited narrower variation in oxygen content compared with that for NdBaMn2O6-delta and NdBaFe2O6-delta. This was explained by a higher distortion of square-pyramidal/octahedral surrounding of 3d-metals in NdBaMnFeO6-delta, which significantly increased with oxygen content, reducing the upper limit of oxygen content down to approximate to 5.45.