Continuous efforts are made to explore alternative methods for reducing Schistosomiasis. So, this study evaluated the effectiveness of Chlorella vulgaris and Pediastrum boryanum extracts carried on their nanocrystalline cellulose (NCC) as immunostimulants for Biomphalaria alexandrina snails against Schistosoma mansoni infection. The results showed that the lowest cercarial shedding/snail was 340 and 330 with 400 mg/L of C. vulgaris extract and NCC + C. vulgaris extract, respectively. Meanwhile, it was decreased with 200 mg/L of P. boryanum extract and 400 mg/L of NCC + P. boryanum extract, with high survival rates for all treatments. In addition, snails treated with 400 mg/L of C. vulgaris extract and 200 and 400 mg/L of NCC + C. vulgaris extract showed a significant decrease in the contents of hydrogen peroxide (0.639, 0.426, and 0.564 mM/L), respectively, compared to the control group (0.695 mM/L). Furthermore, C. vulgaris extracts induced numerous hemocytes around immature cercariae and sporocysts. P. boryanum extracts showed degenerated sporocysts surrounded by plenty of hemocytes. Nanocellulose carriers improved the delivery of microalgal components within B. alexandrina snails, causing the cercariae to lose their ideal shape. Gas chromatography-mass spectrometry (GC–MS) analysis revealed that C. vulgaris and P. boryanum extracts contained oleic acid, which improved the immunological response of snails, and glutamic acid and flavonoids acted as immune modulators and antioxidants. Ultimately, the toxicity assay indicated that NCC + C. vulgaris extract and NCC + P. boryanum extract were the safest for Artemia salina as a non-target aquatic organism. © 2024 Elsevier B.V.