Abstract: The dislocation configuration and the interaction between hydrides and dislocations of N18 Zircaloy after cyclic deformation at room temperature have been investigated,using transmission electron microscopy.The results show that there existed many dispersing precipitated particles in N18 Zircaloy,and that the dislocation configuration was characterized by dislocation lines pinned by precipitate particles whichThe dislocation configuration and the interaction between hydrides and dislocations of N18 Zircaloy after cyclic deformation at room temperature have been investigated,using transmission electron microscopy.The results show that there existed many dispersing precipitated particles in N18 Zircaloy,and that the dislocation configuration was characterized by dislocation lines pinned by precipitate particles which were formed by { 10$\overline{1}$ 0} prismatic slip.In the process of deformation,only part of grains deformed plastically while the others were in elastic state.The hydrides in N18 Zircaloy specimen were mainly composed of δ phase zirconium hydrides with F.C.C structure.Hydrides had a “size effect” on dislocation motion,i.e.the hydrides in small size could be cut open by dislocation slip while those in big size could not.