The invention refers to the polymorphic forms of rifaximin, namely to forms of rifaximin α, β, γ.The polymorphic form of rifaximin α has a water content lower than 4.5% and produces a powder X-ray diffractogram showing peaks at values of the diffraction angles 2θ of 6.6°； 7.4°； 7.9°； 8.8°； 10.5°； 11.1°； 11.8°； 12.9°； 17.6°； 18.5°； 19.7°； 21.0°； 21.4°； 22.1°.The polymorphic form of rifaximin β has a water content higher than 4.5% and produces a powder X-ray diffractogram showing peaks at values of the diffraction angles 2θ of 5.4°； 6.4°； 7.0°； 7.8°； 9.0°； 10.4°； 13.1°； 14.4°； 17.1°； 17.9°； 18.3°； 20.9°.The polymorphic form of rifaximin γ has a water content between 1.0% and 2.0% and produces a powder X-ray diffractogram showing a mainly amorphous profile and few significant peaks at values of the diffraction angles 2θ of 5.0°； 7.1°； 8.4°.The invention also relates to processes for the production thereof, wherein by heating the raw rifaximin is dissolved in ethyl alcohol in order to cause the beginning of the crystallization of product by addition of water at a fixed temperature and for a fixed period of time, followed by drying under controlled conditions until a precise water content is reached in the end product.The obtained forms of rifaximin are used as medicaments with antibiotic action for the oral and topical use.Invenţia se referă la forme polimorfe de rifaximină, şi anume la formele α, β, γ.Forma polimorfă α de rifaximină are un conţinut de apă mai mic de 4,5% şi o difractogramă a pulberii cu raze X manifestând vârfuri la valorile unghiurilor de difracţie 2θ 6,6°； 7,4°； 7,9°； 8,8°； 10,5°； 11,1°； 11,8°； 12,9°； 17,6°； 18,5°； 19,7°； 21,0°； 21,4°； 22,1°.Forma polimorfă β de rifaximină are un conţinut de apă mai mare de 4,5% şi o difractogramă a pulberii cu raze X manifestând vârfuri la valorile unghiurilor de difracţie 2θ 5,4°； 6,4°； 7,0°； 7,8°； 9,0°； 10,4°； 13,1°； 14,4°； 17,1°； 17,9°； 18,3°； 20,9°.Forma polimorfă γ de rifaximină are un conţinut de apă între 1,0
