The in vitro evaluation of a series of 8.O.4'-neolignans (in their ketone, alcohol, and acetylated forms) on the proliferation of Trypanosoma cruzi led to the detection of three compounds with interesting activities against T. cruzi epimastigotes. These compounds also inhibited the in vitro differentiation of epimastigotes to trypomastigotes. When tested against HeLa cells, the same compounds did not affect the cell vitality and showed a low influence on cell viability as measured by dimethylthiazol diphenyltetrazolium bromide reduction. The three phenylpropanoid moieties tested did not show any activity against T. cruzi. One of the tested compounds, compound 4 (3,4-methylenedioxi7-oxo-1'-allyl-3',5'-dimethoxy-8.O.4'-neolignan) showed the best performance in both trypanocide and cytotoxic assays, suggesting that it should be considered as a leading structure for further research.