The temperature dependence of the in-plane magnetic anisotropy of Co/Cu(1117) has been studied by means of the magneto-optic Kerr effect. Strong variations of uniaxial and biaxial anisotropy contributions are found during the first heating. At two different temperatures the uniaxial anisotropy crosses zero causing a change of magnetic behavior. A correlation between the anisotropy behavior and the temperature dependence of the differential susceptibility is apparent. The susceptibility maxima appear at the temperatures where the magnetic anisotropies become negligible small.