Advancement in drug delivery could come from innovate improvement to existing drug delivery system. Because of reduce frequency of administration, sustain release dosage from enjoy convenience and ambulatory patient compliance. Ethyl cellulose is a unique nonbiodegradable, water soluble and pH independent polymer used in sustained release preparations. Different viscosity grade of Ethyl cellulose use for the preparation of sustained drug release from dosage form. Terbutalin sulphate is a model drug use for the treatment of Asthma. To optimize the process variables in the preparation of terbutalin sulphate loaded different viscosity grade 10 cps (EC10) and 45 cps (EC45) ethyl cellulose microspheres were prepared by w/o/w emulsion solvent evaporation technique for the sustained release effect. The results showed that the effect of different viscosity grade of ethyl cellulose polymer and drugs polymer ratio was found to be significant on different dependent parameters. Higher viscosity grade (EC45) found having excellent sustain release effect for longer period of time than lower viscosity grade (EC10) micro spheres. Therefore it can be conclude that TBS loaded microspheres made up of EC 45 viscosity grade may useful in promoting the prolonged release of drug for effective treatment of bronchial asthma.