In recent years scientific and technological advancements have been made in the research and development of rate-controlled drug delivery system by overcoming physiological adversities such as short gastric residence time (GRT) and unpredictable gastric emptying time (GET). Several approaches are currently utilized in the prolongation of GRT, including floating drug delivery system (FDDS), also known as hydrodynamically balanced system (HBS), swelling and expanding system, polymeric bioadhesive system, modified shape system, high density system, and other delayed gastric emptying devices The aim of work was to improve the oral bioavailability of the poorly water soluble drug by incorporating in floating drug delivery system. For better absorption and enhanced bioavailability of some drug, prolongation of retention time of the dosage form in the stomach is essential. In the present study Ritonavir was selected as model drug as it is the prototype antiviral agent used to treat various types of herpes infections having short half-life (2.5-3.3 hours) and low bioavailability (15-30%) in the upper part of GIT hence, it is suitable for gastro-retentive system. Ethyl cellulose was used to achieve the controlled delivery of drug from polymer matrix and emulsion solvent diffusion technique is selected for formulation. The particle size of floating microspheres shows different size for different formulation; this may due to variation in the composition of formulations. The mean particle size for all formulations was in the range of 135.103 – 229.418mm.