Mechanical properties of ultrafine grained (UFG) zirconium (grain size 200 nm), produced by a combination of extrusion, wire drawing and specific annealing, were studied at temperatures 4.2 - 300K in uniaxial compression and compared with coarse grained (CG) Zr. In parallel, investigations by X-ray diffraction (texture) and transmission electron microscopy were undertaken in order to reveal the evolution of the microstructure with increasing strain. Volume fractions of twins have been determined for UFG and CG Zr. It has been found that the activity of twinning is smaller in UFG Zr in comparison with CG Zr at ambient and lower temperatures, but the contrary is true for very low temperatures (4.2K), where twinning increases with decreasing grain size. The influence of twinning on mechanical properties of UFG Zr has been discussed, too.