Six new indole alkaloids including five new glyantrypine derivatives (1, 2a, 2b, 3, 4) and a new pyrazinoquinazoline derivative (5), together with eight known alkaloids (6−13), were isolated from the culture of the mangrove-derived fungus Cladosporium sp. PJX-41. Their structures were elucidated primarily by spectroscopic and physical data. The absolute configurations of compounds 1−9 were established on the basis of CD, NOESY data, and singlecrystal X-ray diffraction analysis. Compounds 2b, 5, 7−9, and 11 exhibited significant activities against influenza virus A (H1N1), with IC50 values of 82−89 μM.