To report the effectiveness of various concentrations of garlic juice on inhibition zone of Gram-positive bacteria isolated from tiger shrimps. Four concentrations of garlic juice used in this research were: 0%, 12.5%, 25% and 50%. Two different bacteria were successfully isolated from tiger shrimps categorized as Gram-positive. The bacterial inhibition zone revealed that garlic juice could inhibit the growth of these bacteria in the form of clear zone on media. The average diameters of inhibition zone from those two bacteria were significantly increased in garlic juice receiving group compared with the control (untreated) group (P < 0.05). For bacteria B, this increase was dose dependent manner. These findings demonstrated the potential of garlic as a natural alternative to currently used antibacterial agent for Gram-positive infection in the tiger shrimp.