Five diterpenoid-derivative alkaloids, lycoctonine (1), 18-O-methyllycoctonine (2), delcosine (3), 14-acetyldelcosine (4), and 14-acetylbrowniine (5), were screened for their antibacterial, antifungal, and antiviral activities. Both DNA virus Herpes simplex (HSV) and RNA virus Parainfluenza (PI-3) were employed for antiviral assessment of the compounds using Madin-Darby bovine kidney and Vero cell lines. Their maximum non-toxic concentrations (MNTC) and cytopathogenic effects (CPE) were determined using acyclovir and oseltamivir as the references. Antibacterial and antifungal activities of the alkaloids were tested against Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Acinetobacter baumannii, Staphylococcus aureus and Bacillus subtilis, as well as the fungus; Candida albicans by microdilution method as compared to the references ampicilline, oflaxocine, and ketacanazole. The alkaloids presented a notable antibacterial effect only towards K. pneumoniae and A. baumannii (8 μg/ml), while they had quite considerable antifungal activity at 4 μg/ml concentration. On the other hand, the alkaloids were found to have selective inhibition against PI-3 virus ranging between 1 and 32 μg/ml as minimum and maximum CPE inhibitory concentrations, whereas they were completely inactive towards HSV. ©ARKAT USA, Inc.