The structure, hardness, and elastic modulus of Pd/Ti multilayers deposited by radio-frequency magnetron sputtering were investigated by x-ray diffraction, high-resolution transmission electron microscopy, and nanoindentation. Both the Ti and Pd layers were face-centered-cubic structures in all modulation periods from 2.8 nm to 90.0 nm in Pd/Ti multilayers. There are stacking faults in Ti layers at large modulation periods, where the crystal. structure is hexagonal close packed. An anomalous hardness enhancement was observed. The hardness values of Pd/Ti multilayers are three times and two times the values measured in Pd films and as calculated by the rule of mixture for Pd and Ti films, respectively. The modulus values of Pd/Ti multilayers are between those of constituent single layer films at a larger modulation period, and increase slightly at a smaller modulation period. The elastic modulus. difference model cannot explain this hardness enhancement, since the elastic modulus is almost the same for the constituent materials in the Pd/Ti multilayers. The hardening mechanisms in the multilayers have been discussed. (C) 2003 American Vacuum Society.