Thin films of the colossal magnetoresistance material La 1-xSrxMnO3 (LSMO) grown on SrTiO3 substrates exhibit bi-axial magnetocrystalline anisotropy with easy axes along the  and [11̄0] directions. We have recently discovered that the intrinsic biaxial magnetic anisotropy combined with a giant planar Hall effect lead to striking switching behavior in the transverse resistivity of LSMO films (Appl. Phys. Lett. 84, 2593 (2004)). Here we use this phenomenon as a sensitive tool for measuring in-plane magnetization in order to characterize the magnetic anisotropy.