Electrodeposition of Ni on atomically flat H-terminated Si(111) surfaces in aqueous acidic solutions containing Ni2+ ions produced rodlike Ni clusters 20-80 nm wide, 5-20 nm high, and more than 1 mum long, nearly in the [(11) over bar2] direction. Such aligned Ni nanorods were formed where the H-Si(111) surface had regularly arranged step lines, indicating that the morphology of the Si surface plays an important role in the Ni-rod formation. Detailed analyses of atomic force microscopy images revealed that the Ni nanorods started to grow from dihydride step edges of the H-Si(111) surface and extended along lines connecting the dihydride step edges. The cross section of the Ni rods suggested that they grew epitaxially on H-Si(111).