Three new phenazine derivatives, named izumiphenazines A-C (1-3), and the known phenazine-1,6-dicarboxylic acid (4) were isolated from Streptomyces sp. IFM 11204. The structures of the isolated compounds were elucidated by means of spectroscopic methods including UV, IR, HRESIMS, and 1D and 2D NMR. Compounds 1-3 were evaluated for their activity in overcoming TRAIL (TNF-related apoptosis-inducing ligand) resistance in human gastric adenocarcinoma cells. Compounds 2 (30 μM) and 3 (20 μM) in combination with TRAIL showed synergistic activity in sensitizing TRAIL-resistant AGS cells.