<jats:title>Abstract</jats:title><jats:p>Three new indole‐containing diketopiperazine alkaloids, named variecolorins M–O (<jats:bold>1</jats:bold>–<jats:bold>3</jats:bold>), together with the eight known analogues <jats:bold>4</jats:bold>–<jats:bold>11</jats:bold>, were isolated from a deep‐ocean sediment‐derived fungus, <jats:italic>Penicillium griseofulvum.</jats:italic> Their structures were determined by analysis of the spectroscopic data. The 2,2‐diphenyl‐1‐picrylhydrazinyl (DPPH) radical‐scavenging activities and the cell‐proliferation inhibitory activities of the three new compounds <jats:bold>1</jats:bold>–<jats:bold>3</jats:bold> were investigated.