The density distributions in the axial and radial cross sections of two typical sodium sulfur cells were obtained by a high-energy x-ray computed tomography (CT) system with a linear accelerator. The tomograms of the low-resistance cell showed a uniform density distribution of sulfur and sodium pentasulfide in the graphite felt of the sulfur electrode, while those of the high-resistance one were indicative of a nonuniform density distribution. The difference in the cell characteristics between the cells could be; accounted for by the difference in the density distribution of the active material in the sulfur electrode. The low discharge voltage of the high-resistance cell, calculated using an internal-parallel-cell model, agreed well with experimental results. The tomograms of cells taken by x-ray CT can ise applied to evaluate sodium sulfur cell characteristics.