Synucleinopathies are neurodegenerative pathologies in which disease progression is closely correlated to brain accumulation of insoluble a-synuclein, a small protein abundantly expressed in neural tissue. Here, two types of modified polypropyleneimine (PPI) dendrimers having either urea or methylthiourea (MTU) surface functional groups were investigated in a cellular model of synucleinopathy. Dendrimers are synthetic macromolecules that may be produced in a range of well-defined molecular sizes. Using cellomics array scan high-content screening, we show that both types of dendrimers are able to significantly reduce intracellular levels of a-synuclein aggregates dependent on the concentration, the type and molecular size of the dendrimer with the bigger size MTU-dendrimers having the highest potency. The intracellular clearance of a-synuclein aggregates by dendrimers was achieved at noncytotoxic concentrations.