Purpose: The objective of the present study is to assess the antimicrobial activity of gastroretentive formulation for moxifloxacin HCl and in vitro antimicrobial evaluation using the cup-plate method. Materials and Methods: Gastroretentive floating tablets of moxifloxacin HCl were prepared using variable amounts of hydroxypropyl methylcellulose (HPMC) K100M and Lannea coromandelica gum (LCG) by direct compression technique. Results and Discussion: Formulations were developed, optimized, and are checked for pharmacopoeial tests. Results show that all batches were lain within the standard limits. Further, in vitro drug release was assessed formulation (FS5) by antimicrobial assay using Staphylococcus aureus and Escherichia coli as test microorganisms. Results reveal that released drug effective against both organisms for 24 h represents good antimicrobial activity. The minimum inhibitory concentration was founded to be 10 μg/mL. Conclusion: Formulation (FS5) containing 50 mg of HPMC K100M and 50 mg of LCG expected to improve patient compliance by means of providing a good clinical outcome.