This work evaluated the effects of dietary supplementation with the seaweed, Pterocladia capillacea, nanoparticles (SN) on the growth, whole-body composition, digestive enzyme activities, feed efficiency, immunological response, antioxidant activity, and gene expression of the whiteleg shrimp, Litopenaeus vannamei. The SN form was conducted using a Planetary Ball Mill PM 400. The particle size of the SN was verified through Dynamic Light Scattering (DLS) analysis. The DLS showed that the mean particle sizes of SN were between 151 nm (13.6%) and 835 nm (64%). Throughout 60 day experimental trial, postlarvae (PLs) of L. vannamei were subjected to one of the following five feeding groups. The first group is a commercially available shrimp feed as a basal diet without any seaweed supplementation, functioning as a negative control (C0%). A second group received the commercial feed supplemented with 2% (20 g/kg) dried seaweed powder (SP2%), functioning as a positive control. The remaining three shrimp groups were fed diets supplemented with seaweed nanoparticles (SN) at concentrations of 0.5% (SN0.5%), 1% (SN1%), and 2% (SN2%), respectively. 750 postlarval (0.053 g/PL) were allocated to five experimental diet groups. Each group consisted of 150 PLs (triplicate). The PLs were fed their corresponding regime three times a day at 10% of their body weight. The results revealed that, compared with those of the positive (C0%) or negative (SP2%) controls, with the increasing dietary supplementation levels of SN, especially SN2%, the growth (FW, WG, and SGR), digestive enzymes (amylase and lipase activities), carcass composition (protein and lipid contents), nutrient efficiency (FI, PI, FER, FCR, and PER), antioxidant activities (SOD and CAT), innate immunity activities (LYS and MDA), and related-immunity gene expressions (p53) of L. vannamei were significantly improved. In conclusion, these findings concluded that applying nanotechnology tools enhances feed additives and significantly maximizes the positive effects of these additives on L. vannamei growth, health, and overall production. Further research is required to understand and explain how seaweed nanoparticles affect these shrimp’s physiological state and upgrade some immune-related gene expressions.