Intracellular abnormal protein deposits, such as tau, α-synuclein and TDP-43, are the hallmark of many neurodegenerative diseases, and the distributions of these pathological proteins are closely correlated with disease symptoms and progression. A growing body of evidence strongly suggests that these abnormal proteins have prion-like properties: they convert normal proteins into abnormal forms, self-propagate through neuronal networks, and then spread in the brain. This prion-like propagation of abnormal proteins may account for the diversity, selective degeneration and disease progression seen in neurodegenerative diseases, although the molecular mechanism remains uncertain the molecular details of this mechanism. This review describes recent studies on prion-like properties of abnormal proteins in vitro, in cells and in animal experimental models.