Abstract The genus Senecio from Patagonia, Argentina, contains several species, including Senecio coluhuapiensis. In the present study, we isolated 1-heneicosanol from this angiosperm. The structure of 1-heneicosanol was established on the basis of spectroscopic analysis and bibliographical data, and its microbiological activity evaluated. 1-heneicosanol presented activity against Staphylococcus aureus (ATCC 29213) and Pseudomonas aeruginosa (ATCC 27853) as well as against Candida albicans (NIM 982879) and C. krusei (ATCC 6258), at a concentration of 250 µg/ml for all species. The most active concentration of pure compound for reducing the germinative tube of the phytopathogenic fungus Botrytis cinerea was 80 µg/ml.