A new ternary ruthenium oxide Na2RuO4 was prepared and shown to crystallize with a new structure type. Single crystal X-ray diffraction measurements reveal that Na2RuO4 consists of RuO4 chains made up of RuO5 trigonal bipyramids by sharing axial corners. Na2RuO4 is a magnetic semiconductor with a variable range hopping behavior, and its molar magnetic susceptibility chi(mol) has a broad maximum at similar to74 K. The derivative d(chi(mol)(.)T)/dT exhibits a peak at 37.7 K which has been confirmed by heat capacity measurement to be due to long-range antiferromagnetic ordering.