A new method to prepare nanocrystalline alloys was developed by means of crystallization from amorphous alloys. By using this method, a Ni‐P alloy with 9 nm crystallites was synthesized. The structures and grain sizes of the alloy were examined by means of x‐ray diffraction, transmission electron microscopy, and high resolution electron microscopy. Specific heat capacity and thermal expansion coefficient of the nanocrystalline Ni‐P alloy prepared by this method were found to be greater than those of the coarse‐grained crystalline alloy by 12.3% and 56.2%, respectively. A new micromechanism for nanometer‐sized crystallites formation is discussed.