Saxitoxins (STXs) are a highly marine neurotoxins derived from harmful algal blooms and cause paralytic shellfish poisoning (PSP) that pose a significant risk to public and environmental health. The study of STXs toxicity has been carried out but little and is known about the histopathological responses on mice. The purpose of this study was to evaluate immunotoxic and histological responses induced by STXs extracted from Acanthocardia tuberculatum. To this end, daily, mice were treated orally during 7 days with sublethal concentrations (10 mg /100 g mouse). Lymphocyte proliferation and brain histopathology were analysed after treatment. The results showed a significative increase of lymphocytes level and a decrease of polynuclears level. The histological study in brain mice showed an increase of the number of the nucleus as well as a hypercondensation of the chromatin brain, Also, we observed the presence of some multinucleated giant cells that indicate the inflammation in brain. We conclude that STXs induce inflammation and cells necrosis in brain mice and causes the importation of the immunizing cells and the development of the inflammatory reactions.