The concentration and temperature dependencies of magnetic anisotropy in the quasiteraary (Y1-xThx)2Fe14B system have been studied on aligned powders. With increasing Th content, the enhancement of the uniaxial anisotropy at low temperatures (K1 at 4.2 K increases from 0.8 MJ m-3 for x = 0 to 1.5 MJ m-3 for X = 1) and the change in K1(T) behaviour from anomalous characteristic for Y2Fe14B to the monotonous decrease with increasing temperature have been found.