The study was aimed to determine the antibacterial effect of crude and aqueous extract of garlic (Allium stivum) against standard strain of Pseudomonas aeruginosa ATCC 27853. An interventional study was conducted in Department of Pharmacology and Therapeutics in collaboration with Department of Microbiology, Mymensingh Medical College, Mymensingh. The minimum inhibitory concentration (MIC) of aqueous garlic extract (AGE) and antibiotic Imipenem were also determined with the help of broth dilution method. Inhibitory effect of crude garlic extract (CGE) was determined by inoculation of bacteria in CGE incorporated nutrient agar (NA) media and for AGE antibacterial effect was determined by disc diffusion method. All experiments except disc diffusion procedure were reconfirmed by subculture in pure NA media. In case of CGE the growth inhibition of test organism was observed in 30% CGE incorporated NA media. On the other hand sensitivity of AGE also determined in disc diffusion and the zone of inhibition (ZOI) was 7 mm, 12 mm and 20 mm at 25 μg/10 μl, 50 μg/10 μl and 100 μg/10 μl concentrations respectively. The MICs of AGE and Imipenem were 600 μg/ml and 1μg/ml. The MIC of imipenen was far less in comparison with the MIC of AGE. From the findings it is clearly determined that both the extracts have definite antibacterial effect upon Pseudomonas aeruginosa. Further studies are required to detect and isolate the active ingredients present in the Garlic extract responsible for antibacterial effect. Then their effects against the studied organism should be studied in vivo separately and its toxicity profile should also be taken into account. Only then the Garlic extracts fulfilled the criteria for its therapeutic use. Still then external application advised for burn and superficial skin infections and may be used in food poisoning, and respiratory tract infection along with conventional antibiotics which are used in those conditions.