Two new sulfur-containing phenolic compounds, 7-hydroxy-5-hydroxymethyl-2H-benzo[1,4]thiazin-3-one (1) and 2,5-dihydroxy-3-methanesulfinylbenzyl alcohol (2), along with two known compounds, 3-chloro-2,5-dihydroxybenzyl alcohol (3) and 2-hydroxy-6-methylbenzoic acid (4), were isolated from the mycelial solid culture of a soil-derived Ampelomyces fungus by antibacterial assay-guided fractionation. Their structures were elucidated on the basis of spectroscopic analysis. Compounds 1-3 showed structure and microbial dependent antibacterial activities.