Kaurenoic acid (KA), a kaurane-type diterpene extracted from leaves of Mikania hirsutissima, was previously reported as an inhibitor of vascular contractility mainly by blocking extracellular Ca²⁺ influx. The compound is known for several other biological activities such as antiparasitic, antispasmodic and antibacterial activity. The aim of the present study was to investigate the effect of KA on Aspergillus nidulans. KA (0.3 mM) showed fungistatic activity against A. nidulans with visible hyphal elongation and morphology damage. These effects were reverted by CaCl₂ addition showing that KA interferes with intracellular Ca²⁺ gradient in A. nidulans. This is the first report on the mechanism of action of KA involving calcium levels by altering the elongation of fungi hyphae.