Cellular protein degradation systems are necessary to avoid the accumulation of misfolded or damaged proteins. Deficiency in these systems might cause to partial degradation of misfolded proteins and generation of amyloidogenic fragments. Protein misfolding is believed to be the primary cause of neurodegenerative disorders such as Alzheimer's disease (AD). In this study, we investigate effect of two anionic peptide fragments including, an acidic fragment of human Aβ (Aβ1-11) and a phosphorylated fragment of β-Casein (Tetraphosphopeptide), on tau protein aggregation. According to our results, these peptide fragments, induced tau fibrillization in vitro. In sum, we suggest that structural and conformational characters of inducer are as important as charge distribution on anionic inducer molecules however more experiments would be need to exactly confirm this suggestion.