Both seismic and geodetic data suggested that the ∼120-km long Weifang segment of the Tanlu fault zone, a large-scale active strike-slip system at east China, is a seismic gap with no obvious along-strike shear motion at surface. Measuring crustal deformation around the segment is crucial to constrain stress/strain buildup and potential seismic risk at the fault. We measured crustal and upper mantle seismic anisotropy using P-to-S converted waves at the Moho (Pms) and core-mantle boundary (SKS) recorded by broadband arrays across the Weifang fault segment. The measured crustal anisotropy inside the fault zone shows a fast direction of ∼NNE, parallel to the fault orientation. Right east to the fault zone, the fast axis rotates by almost 90° to ESE. The crustal anisotropy within the fault zone could be caused by aligned microcracks and foliated minerals due to long-lasting shear motion inside the fault zone.