Purpose: Formulation and evaluation of annon irritant ion activated in situ gel of a flouroquinolone antibiotic, Gatifloxacin. Methods: Ion activated in situ gel formulation was developed using Gellan gum as phase transition polymer and HPMC K 100M as release retardant which can undergo a sol-gel transition in the cul-de-sac of the eye. Results:Gatifloxacin in situ gel formulation with pH 6.0-6.3 and 52 cps in solution form resulted in gel formation in simulated lacrimal fluid having 325 cps viscosity, indicating phase transition behaviour in physiological conditions of eye. It was found to be isotonic, as it exhibited no change in the size and shape of RBCs. Formulation was found to be non irritant to eyes exhibiting mean score of zero in HET-CAM (Hen?s Egg Test ChorioAllantoic Membrane) test for ocular irritancy for 5 min Conclusion: It can be concluded that the developed in situ gel formulation can be viewed as a better alternative to the conventional eye drops of Gatifloxacin by virtue of its ability to enhance pre corneal residence time and consequently ocular bioavailability with lesser frequency of administration.