A new isobenzofuranone derivative, (R)-3-acetyl-[5,7]-dimethoxy-3H-isobenzofuran-l-one (1), together with six known compounds, (R)-3-acetyl-7-hydroxy-5-methoxy-3H-isobenzofuran-l-one (2), banksialactone D (3), (3R,4S)-3,8-dihydroxy-3-hydroxymethyl-6-methoxy-4,5-dimethyl-isochroman-1-one (4), 1-O-[α-L-rhamnopyranosyl]-2,5-dimethyl-3-phenol (5), p-hydroxybenzaldehyde (6), 2-(4-hydroxyphenyl) ethanol (7), were isolated from Arctic fungus Gyoerffyella sp. CPCC 401434. Their structures and absolute configurations were elucidated by the analysis of spectroscopic data, electronic circular dichroism, and comparison with reported literature data. Herein, all compounds were reported for the first time from the genus Gyoerffyella and their cytotoxic and antibacterial activities. [ABSTRACT FROM AUTHOR]