The present investigation deals with the formulation and evaluation of sodium alginate based In situ gel of Amoxicillin. Sodium alginate was used as a polymer and CaCO3 was used as a cross-linking agent. The objective of this study was to Study of Effect of Sodium Alginate & Calcium Carbonate Composition Difference on In Situ Gelling Gastro retentive Amoxicillin Liquid Formulation. Gelling capacity was evaluated based on a graded response which indicates rapidity of gelation and time taken by the gel to dissolve. All the formulations showed instant gelation but with regard to integrity, all formulations except the one with lowest SA level formed stiff gels maintaining integrity for at least 12 hr. With respect to floating behavior, all formulations except the one with the lowest SA level floated for more than 12 hr irrespective of their composition. Most of the formulations took less than 1 min to float but those with the lowest SA and CaCO3 levels floated after about 2 min. The formulations showed satisfactory content uniformity and pH ensuring their safe use. The rheological studies showed that the formulations possessed optimal viscosity which can facilitate easy administration of the required dose. Drug release study revealed release retarding behavior of the formulations and noticeable burst release. This effect was reduced at higher concentration of SA and CaCO3. Release retarding effect of SA was only marginal at higher concentrations. CaCO3 showed a similar effect but at higher levels insignificant change in release was observed. The study demonstrated that release rate of amoxicillin was depends on the amount of sodium alginate and CaCO3 used.