A remarkably giant intrinsic magnetostriction λ111 as high as 6700 ppm was found at 70 K in PrFe1.9 compound, which is much larger than the value of 5600 ppm predicted by single-ion theory. Change of the easy magnetization direction from [111] to [100] with decreasing temperature occurs between 30 and 70 K, which was verified by step-scanned {440} and {222} X-ray diffraction reflections. It was further demonstrated that this compound has a rhombohedral symmetry between 70 and 300 K, and a tetragonal symmetry between 15 and 30 K. Therefore, the magnetostrictive anomaly at low temperature may be interpreted by the spin reorientation transition of the compound. PrFe1.9 with high magnetostriction is a good candidate material for magnetostriction applications at low temperature.