Tau protein plays a major role in Alzheimer's disease. The tau protein loses its functionality by self-aggregation due to the two six-amino acid sequences VQIVYK and VQIINK of the protein. Hence it is imperative to find therapeutics that could inhibit the self-aggregation of this tau peptide fragments. Here， we study the inhibitory potential of a cationic polymer polyethyleneimine (PEI) and a cationic polypeptide arginine (Arg) on the aggregation of VQIVYK， and GKVQIINKLDL peptides， and tau mutant protein (P301L)， found frequently in taupathy. Various characterization methods are employed including thioflavin S， transmission electron microscopy， and dynamic light scattering to study the aggregation/inhibition process in vitro. Results show that PEI and Arg significantly inhibit tau peptides and protein aggregation. The study could be applied to understand tau protein aggregation mechanism in the presence of cationic polymers.