Neutron diffraction studies have been carried out on a single crystal of oxygen-deficient perovskite NdBaCo 2 O 5 in the temperature range of 7-370 K. There have been observed, with decreasing temperature T, two magnetic transitions accompanied with structural changes, to the antiferromagnetic phase at ~360 K and to the charge ordered antiferromagnetic one at ~250 K. We have studied the magnetic structures at 300 K and 7 K. At these temperatures the Co-moments have the so-called G -type antiferromagnetic structure, and Co ions are considered to be in the high spin state over the whole temperature range below T N~3 60 K irrespective of whether the charge ordering is present or not.

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