Single crystals of UNi 1 - x Sb 2 have been grown from an Sb-rich melt and studied by means of X-ray diffraction, magnetic and electrical transport measurements. Crystal structure refinements indicated significant deficiency on the transition metal sites in the tetragonal HfCuSi 2 -type unit cell, yielding the actual composition UNi 0 . 5 Sb 2 . The single crystals studied order antiferromagnetically below T N =161K and exhibit another phase transition at T t =60K, presumably caused by a spin-reorientation. No crystal structure distortion could be detected at 10 K. Above T N the electrical resistivity is dominated by a Kondo effect, whereas at lower temperatures it shows a behavior characteristic of antiferromagnets. The overall magnetic and electrical transport properties of UNi 0 . 5 Sb 2 are highly anisotropic both in the ordered and paramagnetic states.