Values of oral lethal dose of aluminum (Al) nitrate are extremely different and rare in the literature. The study is an attempt to determine the oral LD50 of aluminum nitrate in the Wistar rats and to measure the effect of the high doses of this aluminum compound on rats’ different organs, on acetylcholinesterase (AChE) activity, and on acetylcholine (ACh) levels in the hippocampus. Four groups of male Wistar rats are used (n = 28). The treated groups receive three doses of aluminum nitrate (Al1 = 2,500 mg/kg, Al2 = 3,500 mg/kg, and Al3 = 4,500 mg/kg) once by gavage, while control rats receive tap water. All rats are examined twice daily for mortality and impairment during the 2-week experiment. The bodyweight (BW) is measured at the beginning and at the end of the experiment. Dissection is realized for each dyed rat and the dosage of AChE activity and ACh levels isrealized at the end of the experiment by colorimetric method. The obtained results show that the higher dose (Al3) kills 30% of the rats under study and causes spleens’ dark discoloration in the dyed rats. Both Al2 and Al3decrease significantly the spleen weight (p < 0.01) and AChE activity (p < 0.01), but increase significantly the ACh levels (p < 0.01 and p < 0.001, respectively), in hippocampus of rats. Even if the lethal dose of aluminum nitrate is not reached, the effect of the high acute doses on viscera and cholinergic system is demonstrated.