Sixteen compounds were isolated from the solid rice culture of the endophytic fungus Alternaria alstroemeriae WZ-419 derived from Pseudostellariae Radix, using silica gel, ODS, Sephadex LH-20 column chromatography, and preparative HPLC. Their structures were elucidated based on physicochemical properties and comprehensive spectroscopic analyses, and identified as alterpenoid A (1), tricycloalternarene A (2), altenusin (3), 4'-epialtenuene (4), altenuene (5), alternariol (6), altenuisol (7), 3-hydroxyalternariol-5-O-methylether (8), alternariol-9-methyl ether (9), alternariol 1′-hydroxy-9-methyl ether (10), stemphyperylenol (11), dihydroalterperylenol (12), alterinone A (13), 4-hydroxy-3-methoxy-5-(2E,6E-3,7,11-trimethyldodeca-2,6,10-trien-1-yl) benzoic acid (14), hexylitaconic acid (15), and altechromone A (16). Among them, compound 1 and 13 were new, and compounds 14 and 15 were isolated from the genus Alternaria for the first time. The antibacterial activities of compounds 1–16 were evaluated in vitro. Compounds 3, 6–8, 10, 11, 13, and 14 exhibited notable inhibitory effects against Gram-positive bacteria, with minimal inhibitory concentrations ranging from 8 to 64 µg/mL.This study isolated a series of antimicrobial metabolites from the endophytic fungi of Pseudostellariae Radix, providing new insights into their bioactive constituents and laying a foundation for further pharmacological investigations.