Aims: Marine-derived fungi are a potential for the search of new compounds with relevant features. Among these, the ligninolytic enzymes have potential applications in a large number of fields, including the environmental and industrial sectors. This work aimed to evaluate the laccase activity of the marine-derived fungus Alternaria alternata, under various cultivation conditions and its application in synthetic dyes decolorization. Methodology and results: Wheat bran prepared with 40 mL sea water proportion was the most suitable substrate for laccase production (114.06±2.24 U/mL) by A. alternata, after 14 days of incubation in submerged fermentation. Laccase production in static cultivation was superior to that in agitated cultures. The simple Boyd and Kohlmeyer medium with supplementation of 2 mM CuSO4·5H2O on day 6, at an incubation period of 14 days and incubation temperature of 28±2°C under static conditions, yielded amounts of laccase (36.13±0.34 U/mL) less than that obtained with submerged fermentation of wheat bran as unique substrate. Furthermore, A. alternata has high decolorization capability toward azo dyes in the absence of redox mediators, 75.47% of the reactive black at 0.01% concentration, was removed after 30 days of incubation. Also has good ability to decolorize the triphenylmethane dye crystal violet, at 0.01% concentration, about 69.35% of the dye was removed after 30 days. Conclusion, significance and impact of study: These unusual properties demonstrate that the marine-derived fungus Alternaria alternata has potentials in specific industrial or environmental applications.