The present invention relates to an improved and industrially advantageous process for the preparation of Rifaximin with high purity and yield. Particularly the present invention relates to improved processes for the preparation of Rifaximin from Rifamycin O and S. More particularly the present invention relates to a process for the preparation of Rifaximin through 3 halorifamycin S. The present invention further relates to a novel polymorph of Rifaximin and process for its preparation.