The objective of the study was to develop floating in situ gel formulations of Ondansetron that has a narrow absorption window and mainly absorbed in the proximal areas of GIT. These formulations increase the targeted action on bacteria for a longer time that can be used in the treatment of Helicobacter pylori (H. pylori) infections and urinary tract infections. Methods: In situ gel formulations were prepared by varying concentrations of sodium alginate as in situ gel forming bio-degradable polymer and calcium carbonate as a cross-linking agent. The formulations were evaluated for Physical appearance, pH, in vitro drug release, viscosity, in vitro floating behaviour, in vitro gelling capacity and drug content. FTIR was conducted for Ondansetron, excipients used and optimized formulation.