Abstract: The cyanobacterium-symbiotic fungus Simplicillium lanosoniveum was used as materials, and the objective of this study was to optimize the culture condition, purify and characterize a novel antibiotic which exhibitied antibacterial activity against the gram-positive bacteria from Simplicillium lanosoniveum.The suitable medium for this antibiotic production was the modified sabouraud medium containing sucrose 30 g/L and peptone 12 g/L and antibiotic production of Simplicillium lanosoniveum was non-growth-associated. This antibiotic displayed a characteristic absorption peak at 254 nm.The molecular weight of this antibiotic was 163.0182 with a retention time of 4.1031 min when the mobile phase of this antibiotic was a0.02 mol/L carbonate buffer ( p H7.5) containing 5% acetonitrile.Biuret and ninhydrin tests of this antibiotic were negative.The founding of this antibiotic provide the feasibility for the classification of Simplicillium lanosoniveum.