Acinetobacter baumannii being a multidrug-resistant (MDR) pathogen poses great threats to health with mortality ranging from 8% to 35%. As it is resistant to the broad spectrum of antimicrobial drugs, there is a need for alternative therapeutic methods to combat its propagation. Bacteriophages being the natural killer of bacteria are an effective therapeutic agent against A. baumannii. In this research work, a sewage bacteriophage was tested for its therapeutic potential against MDR A. baumannii. To achieve this, albino mice were infected with the bacterium (A. baumannii) and bacteriophage with the appropriate dose, and the mice were observed for 12 days and their hematological and histopathological studies were performed. Hematological studies show that erythrocyte, leukocyte, and platelet count remain comparable with healthy individuals. While histopathological analysis of mice lung tissues also supports these results, bacteriophage is involved in clearing out the infection. So, from these results, it is confirmed that the isolated bacteriophage could act as an effective therapeutic agent against multidrug-resistant A. baumannii. In the future, further research will be designed on using this phage in combination with other A. baumannii-specific bacteriophages and with other antimicrobial drugs for a more potent therapeutic agent against all the variants of A. baumannii.