Seven previously undescribed polyketide derivatives, fusariumtides A-G (1-7), together with three known analogues (8-10), were isolated from the culture extract of Fusarium asiaticum QA-6, an endophytic fungus obtained from the fresh stem tissue of the medicinal plant Artemisia argyi H. Lev. & Vaniot. Their structures were elucidated by detailed interpretation of 1D/2D NMR spectroscopic and mass spectrometric data, and the absolute configuration of compound 1 was established on the basis of X-ray crystallographic analysis and ECD and specific rotation (SR) calculations. The isolated compounds, which possessed a functionalized decalin moiety, were evaluated for antimicrobial activities. Compounds 1 and 10 exhibited broad-spectrum inhibitory activities against nine tested pathogenic bacteria with MIC values ranging from 1 to 64 μg/mL, while compound 8 showed potent inhibitory activities against aquatic pathogens Aeromonas hydrophilia, Pseudomonas aeruginosa, Vibrio harveyi, and V. vulnificus, which were comparable to/or stronger than those of the positive control chloramphenicol.