Cultivation of the fungal strain Eurotium rubrum, an endophytic fungus that was isolated from the inner tissue of the semi-mangrove plant Hibiscus tiliaceus, resulted in the isolation of one new dioxopiperazine alkaloid, 12-demethyl-12-oxo-eurotechinulin B (1), and one new anthraquinone derivative, 9-dehydroxyeurotinone (2), together with ten known compounds including variecolorin J (3), eurotechinulin B (4), variecolorin G (5), alkaloid E-7 (6), cryptoechinuline G (7), isoechinulin B (8), 7-isopentenylcryptoechinuline D (9), 2-O-methyl-9-dehydroxyeurotinone (10), emodin (11), and emodic acid (12). The structures of the isolated compounds were determined by extensive analysis of their spectroscopic data as well as by comparison with literature reports. Some of the purified compounds were evaluated for antibacterial, antifungal, and cytotoxic activities.