A norditerpenoid k4610422 (1), an inhibitor of testosterone-5α-reductase originally discovered from a mesophilic rare actinomycete of the genus Streptosporangium, was isolated from the culture extract of a thermophilic actinomycete Actinomadura sp. The complete 1H and 13C NMR assignment and absolute configuration of 1 were addressed by spectroscopic measurements including NOESY and CD spectra coupled with ECD calculation, which allowed to establish the (5 R,9 S,10 R,13 S)-configuration. Compound 1 was moderately cytotoxic against P388 murine leukemia cells with IC50 30 μM.