Aims This work was performed to characterize new secondary metabolites with neuraminidase (NA) inhibitory activity from marine actinomycete strains. Methods and Results An actinomycete strain IFB-A01, capable of producing new NA inhibitors, was isolated from the gut of shrimp Penasus orientalis and identified as Streptomyces seoulensis according to its 16S rRNA sequence (over 99% homology with that of the standard strain). Repeated chromatography of the methanol extract of the solid-substrate culture of S.seoulensis IFB-A01 led to the isolation of streptoseolactone (1), and limazepines G (2) and H (3). The structures of 13 were determined by a combination of IR, ESI-MS, 1D (1H and 13C NMR, and DEPT) and 2D NMR experiments (HMQC, HMBC, 1H-1H COSY and NOESY). Compounds 13 showed significant inhibition on NA in a dose-dependent manner with IC50 values of 3 center dot 92, 7 center dot 50 and 7 center dot 37moll1, respectively. Conclusions This is the first report of two new (1 and 2) and known (3, recovered as a natural product for the first time in the work) NA inhibitors from the marine-derived actinomycete S.seoulensis IFB-A01. Significance and Impact of the Study The three natural NA inhibitors maybe of value for the development of drug(s) necessitated for the treatment of viral infections.