In nuclear fuel reprocessing, spent nuclear fuel is dissolved by a nitric acid. It is now known that molybdenum and zirconium in fission products react to form zirconium molybdate hydrate (ZMH). ZMH adheres to the inner surface of reprocessing equipment, which affects the extraction efficiency in the subsequent extraction process. Therefore, a new prevention method of ZMH encrustation is required for stable plant operation. In this study, the encrustation amount of ZMH was investigated. Observing the deposition process, it was clarified that ZMH fine crystals were generated and agglomerated, followed by the rapid deposition. The encrustation amount of ZMH decreased as temperature or initial Mo/Zr mole ratio increased, or as the concentration of a nitric acid was reduced.