Abstract: Using saturated solution of new-type ammonium dimolybdate[(NH<SUB>4</SUB>)<SUB>2</SUB>Mo<SUB>2</SUB>O<SUB>7</SUB>]and nitric acid as raw materials,molybdenum trioxide (MoO<SUB>3</SUB>) nanofibers which is about 20 μm in length and 50~200 nm in diameter were successfully synthesized through hydrothermal synthetic process after acidification.MoO<SUB>3</SUB> nanofibers were characteristiced by means of SEM,TEM,and XRD etc..Results showed that sythesized MoO<SUB>3</SUB> nanofibers has uniform size,smooth surface,good dispersive properties and it will have widely potencial application markets in catalyst,flame retardant-and-smoke suppression,and deep molybdenum processing etc..