Abstract: In order to get molybdenum trioxide molybdenum trioxide powder with different morphologies,especially to get molybdenum trioxide nanofiber,using saturated solution of ammonium paramolybdate and nitric acid as raw materials,molybdenum trioxide powders with different micro-morphology were successfully synthesized through changing synthetic parameters of hydrothermal synthetic process in a hydrothermal reactor.Synthesized molybdenum trioxide powders were characteristiced by XRD,SEM,and HRTEM.Results showed that molybdenum trioxide nanofibers could be got which were more than 20 μm in length,50~200 nm in diameter when the heat treatment temperature was more than 150 ℃,acidity coefficient of precursor solution was more than 15,and heat treatment time more than 20 h.Crystal growth direction of molybdenum trioxide nanofibers was (001).Deviating of synthetic process parameters mentioned above,molybdenum trioxide powders with rodlike,platelike,and flakelike micro morphologies could be synthesized. 