Chitosan nanoparticles (CSNPSs) were prepared from noncommercial chitosan of different molecular weights by the ionic gelation methodology. CSNPSs were applied in solid state (g) to observe the bacterial growth of Bacillus halotolerans MCC1, bacteria that appear in the biofilms of the desalinization membranes. Characterization of CSNPS of high (CSNP2), medium (CSNP3), and low (CSNP4) molecular weight (MW) was studied by TGA, DSC, SEM, EDX, DLS, and XRD. The effect of MW onto the formation of CSNPS was investigated as well as the effect of its application (0.01, 0.03, and 0.03 g at 24, 48, and 72 h) in the growth (%) of B. halotolerans MCC1. The results showed that the average size of CSNPS was in the range of 420-600.3 nm. CSNPS were considered amorphous and less thermally stable than the original chitosan where they were produced. Morphologically when the MW decreases, a reduction in the size of the particle was exhibited. When MW increase a reduction in the zeta potential from 45.7 to 29.9 mV was resulted. The essays to observe the growth (%) of B. halotolerans MCC1 indicated that CSNPS applied in solid state allows the growth of the bacteria; when the MW decreases, the growth of the bacteria increases. The maximum and minimum value of growth was obtained at 72 h, with the use of 0.05 g of CSNP4 (16.86%) and 0.05 g of CSNP2 (2.15%), respectively. The use of CSNPS indicates that the inhibitory effect depends on the MW as well as the doses of application.