The ferrimagnet TbFe11Ti (μm = 11μB at 4.2 K, Tc = 560 K) with the tetragonal ThMn12-type of crystal structure undergoes a first-order spin-reorientation phase transition from basal-plane (at low temperatures) to uniaxial (at high temperatures) magnetic anisotropy. The temperature of the transition is extremely sensitive to the magnetic field in the low-field range (from 250 K at 0.3 mT to 325 K at 0.15 T internal field).