Obesity is a growing global health problem that contributes to diabetes, hypertension, cardiovascular diseases, dementia, and cancer. The increased consumption of saturated fats in a high-fat diet (HFD) contributes to obesity, neurodegenerative diseases, long-term memory loss, and cognitive impairment. We tested whether HFD influences adult hippocampal neurogenesis. Male C57BL/6 mice were divided into two groups and maintained on either a normal diet (ND) or HFD. Seven weeks of HFD significantly decreased the numbers of newly generated cells in the dentate gyrus of the hippocampus without neuronal loss. HFD also increased the level of malondialdehyde (MDA) and decreased the level of brain-derived neurotrophic factor (BDNF) in the hippocampus. The toxic effects of MDA were evaluated on neural progenitor cells (NPCs). MDA reduced the growth of NPCs, but BDNF treatment restored NPCs proliferation. The present data indicate that a HFD impairs hippocampal neurogenesis and NPCs proliferation through increased lipid peroxidation and decreased BDNF.