The degradation of n-eicosane by Trichoderma sp. S019, a fungus collected from soil with extensive degradative ability on an agar medium containing n-eicosane, was demonstrated in liquid medium and in soil. Maximal degradation (77%) was obtained when Trichoderma sp. S019 was incubated for 30 days after the addition of 0.1 mM of n-eicosane to the liquid medium while the highest rate of degradation (40%) was obtained in soil with the addition of 1.5% Trichoderma sp. S019. Furthermore, the degradation of n-eicosane was affected by the addition of a carbon source, the addition of a nitrogen source and agitation. n-Eicosane was indeed degraded by Trichoderma sp. S019 because nonadecanoic acid, n-octadecane, hexadecanoic acid, oleic acid and stearic acid, considered to be the intermediates in the biodegradation of n-eicosane, were detected among the reaction products.