In the course of our screening for new antimetabolites from actinomycetes, it was found that strain KM-10329 produced L-1,2,4-triazole-3-alanine. Many synthetic compounds containing the 1H-1,2,4-triazole ring are known, however, their natural occurrence has never previously been reported. Strain KM-10329 was isolated from a soil sample collected at Joetsu-city, Niigata Prefecture, Japan and classified as Streptomyces sp. The compound was isolated via column chromatography (Amberlite IR-120B, Diaion PA-416, Avicel, activated carbon) and purified. Its structure was determined by spectral data (1H/13C NMR, IR, MS) and comparison with authentic D,L-1,2,4-triazole-3-alanine, confirming it as L-1,2,4-triazole-3-alanine (stereochemistry confirmed by specific optical rotation and CD analysis). The strain also co-produces nourseimycin, a proline antagonist. This is the first report of the natural occurrence of a compound containing the 1,2,4-triazole ring, which is structurally related to L-histidine (with nitrogen substituting the 6-carbon) and presents biosynthetic interest.