Synaptic zinc ions (Zn2+) play an important role in the development of vascular dementia (VD) and Parkinson’s disease (PD). In this article, based on our study and many others, we review the mo-lecular pathways by which Zn2+ causes neurotoxicity. Zn2+ influences calcium homeostasis, energy production pathway, production of reactive oxygen species, endoplasmic reticulum stress pathway, and activated protein kinase/c-Jun amino terminal kinase (SAPK/JNK) pathway and consequently exerts neurotoxicity. Furthermore, we searched various crops for substances that protect neurones from neurotoxicity caused by Zn2+ and clarified that carnosine (β-alanylhistidine) may be a therapeutic drug for VD and PD. Here, we also review the molecular mechanisms underlying the role of carnosine as an endogenous protector and its protective effect against Zn2+-induced cyto-toxicity and discuss prospects for future neurodegenerative diseases therapeutic applications of this dipeptide.