Electroless palladium thin films have been successfully deposited on hydrogenated amorphous Si from a palladium-ammine bath. The d.c. magnetron reactive sputtered 18% hydrogenated amorphous silicon (a-Si:H) possessed a hydrogen passivated surface, using an activation step prior to the electroless deposition to obtain a film with good uniformity. The specially prepared hypophosphite-based dilute metal ion bath exhibited good stability at low operating temperatures of 35–50 °C. The morphology and microstructure of the Pd aggregates were characterized by scanning transmission electron microscopy (STEM) and energy dispersive x-ray spectroscopy (EDX), while the Pd aggregates and as-deposited films from the citrate and NH3/NH4Cl baths were examined by scanning electron microscopy (SEM). Marked differences in morphology and distribution of the Pd aggregates on activated a-Si:H and c-Si substrates were observed and discussed. The as-deposited films with higher coverage from the NH3/NH4Cl bath were typically more uniform and crack-free, while those from the citrate bath suffered from incorporated hydrogen, resulting in bare spots, microcracks and local a-Si film peeling. Auger Electron Spectroscopy (AES) revealed a higher amount of co-deposited phosphorus in NH3/NH4Cl bath films than citrate bath films.