Chitosan nanoparticles (CS-NPs) are potential materials for antibacterial application. This study was focused on synthesized CS-NPs from wasted black tiger shrimp shells (Penaeus monodon) and their antibacterial activity. The CS-NPs were synthesized using the ionic gelation method at a variated initial concentration of chitosan (CS). The characterization of CS-NPs includes functional group analysis using Fourier Transform Infra-Red (FTIR), particle size using Particle Size Analyzer (PSA), and surface morphology analysis using Scanning Electron Microscope (SEM). The results show that the degree of deacetylation (DD) of CS-NPs is more than 90%, with the average particle size of CS-NPs being 92.89 nm to 407 nm (which increased with an increasing initial concentration of CS) which is supported from the occurrence of agglomeration (the results of SEM analysis). Antibacterial activity test showed that CS-NPs were more active in inhibiting Gram-positive (S. aureus) bacteria than Gram-negative (E. coli). Therefore, the wasted black tiger shrimp shells are highly suggested as CS-NPs raw materials for bio-application.