Poachers managed to flee with the horn after killing the rhino by using sophisticated weapons.
Forest guards of the park found de-horned carcass of the male rhino.
Poachers have killed four rhinos in Kaziranga this year so far.
Last year, Assam lost at least 16 one horned rhinos which were poached in different areas of the state.
(Reporting by Hemanta Kumar Nath)