Six new isocoumarins, compounds 1–4 and 14–15, two new benzofurans, 16–17, along with nine known isocoumarin analogues, 5–13 were obtained from the mangrove endophytic fungus Talaromyces amestolkiae YX1. Their structures were elucidated by analysis of spectroscopic data. The absolute configuration of compounds 4, 14 and 15 were determined by the modified Mosher's method and comparison of their CD spectra with dihydroisocoumarins described in the literature. The structure of compound 5 was further confirmed by a single-crystal X-ray diffraction experiment using Cu Kα radiation. Compounds 2, 6, 8, and 10 showed α-glucosidase inhibitory activity with IC₅₀ values of 89.4, 17.2, 36.4, and 38.1 μM, respectively. In the antibiotic assay, compounds 16 and 17 exhibited antibacterial activities with MIC values between 25–50 μg mL⁻¹ against the Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Bacillus subtilis.