ABSTRACT. The shrimp necrotizing hepatopancreatitis is caused by a pleomorphic Gram-negative Rickettsialike bacteria known as NHP-B. It is well known that silver is an effective bactericidal, but experiments with aquatic organisms are scarce, even more at nanoparticle level. The objective of this study was to determine the antibacterial effect of silver nanoparticles (AgNP) against NHP-B in the Pacific white shrimp Litopenaeus vannamei. For this, AgNO3 was used as source of silver, and extracts of dried leaves of green tea Camellia sinensis and neem tree Azadirachta indica as reducing agents. Different lots of infected shrimp received 0,5 and 35 μg of AgNP by forced feeding. The differences between the number of bacterial nodules in shrimp hepatopancreas and shrimp mortality relative to the amount of AgNP demonstrated to be effective against this pathogen.