The present invention describes a process of preparing pharmaceutical composition of roxithromycin, which provides release of the active agent in a modified manner over a desire period for the treatment of various types of infections. The process provides a matrix tablet, comprising of roxithromycin with thermo-reversible, rate controlling, not ionic block copolymers which may also enhance the drug solubility and hence imparts improved bioavailability. More particularly, the said invention relates to a unique process of preparing the pharmaceutical compositions of roxithromycin for oral administration.