Numerous natural products have pharmacological activity such that many biologically active compounds have led to the development of cancer chemotherapy drugs. Spilanthes acmella (Asteraceae) is widely cultivated in the State of Pará, Brazil, being employed in folk medicine for its anti-inflammatory, antimicrobial, antioxidant, analgesic, insecticide, and larvicidal properties. However, its cytotoxicity and influence on actin cytoskeleton organisation in tumour cell lines are practically nonexistent. We have verified the cytotoxicity of a hydroethanolic extract of the inflorescence of S. acmella, and examined its effects on the cytoskeleton of tumour cells. Decreasing concentrations of the extract (250, 500 and 1,000 µg/mL) were given to cultures of neoplastic cells (HEp-2). Cytotoxicity was assessed by the MTT test, and the influence on cytoskeleton organisation was examined by fluorescence microscopy. The IC50 of the hydroethanolic extract was 513 µg/mL, confirming the data obtained from the MTT assay that gave high cytotoxicity. The actin cytoskeleton arrangement of HEp2 cells at 500 and 1,000 µg/mL showed depolymerisation of the filaments, causing loss of morphology and consequently compromising cell adhesion.