To identify marine fungus SZX-6 isolated from the inner of Portunus triuberbuculatus with antibacterial activity and to optimize the fermentation conditions of producing antibacterial active substances. Based on its morphological characters and internal transcribed spacer (ITS) sequence analysis results, strain SZX-6 was identified as Aspergillus tubingensis. The optimized fermentation conditions were determined as sucrose 3%, beef extract 1.5%, KCl 0.1%, MgSO₄ 0.02%, old seawater, inoculum size 1%, 28°C, 160 r/min for 8 d by the the one-factor-at-a-time method, the orthogonal matrix method and the time-bioactivity cources assay. The initial identification data demonstrated that the antibacterial active substances were mainly composed of moderate polar components with plentiful quantity and alkaloid-colored. The strain of A. tubingensis being isolated from the seawater-cultured animal was firstly reported here, and its antimicrobial activity was initially invenstigated in this paper.