Our immune system can be exposed to neutral ionizing radiation. This work proposed to investigate the impacts of low-dose fast neutrons on the molecular structure of the lipids of peripheral blood mononuclear cells (PBMCs) as the primary immune cells. The effects have been followed at the time of 0, 2, 4, and 8 days after neutron exposure. Sixty-four female Wistar rats were used in this work. Thirty-two of them were irradiated using a low-dose fast neutron (241AmeBe, 0.2 mGy/h). The other thirty-two were utilized as a control group. The changes in their lipids molecular structure were investigated using Fourier transform infrared (FTIR) spectroscopy. Besides, lipids were extracted, and the total phospholipids contents were estimated. At the time of 2 and 4 days after irradiation, the results showed significant changes in the molecular structure of lipids in those irradiated samples compare with their control samples, and multivariate analysis succeeded in differentiating between control and irradiated rats. In contrast, no alterations between control and irradiated were detected at the time of 0 and 8 days after. The low-dose fast neutron could induce free radicals, which indirectly affect the molecular structure of the lipids and could damage the phospholipids molecules, and the damage could be repaired. (C) 2020 Elsevier Inc. All rights reserved.