One new chromanone derivative, alterchromanone A (1), and four known curvularin-type macrolides (2-5) were isolated from the crude extract of the mangrove-derived endophytic fungus Alternaria longipes. Their structures were elucidated by MS and NMR spectroscopic analyses and by a comparison with data from the literature. The absolute configuration of 1 was assigned by combination of experimental and calculated electronic circular dichroism (ECD) spectra. Compound 1 exhibited 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity with an IC50 value of 56.3 μg ml-1. According to the structural features of these compounds, the plausible biosynthetic pathways of 1-5 were also proposed.