Malachite green residue can affect aquaculture food safety. Bioremediation of contaminated water by enzyme treatment is an environmentally friendly and economical way to remove contaminating substances. In the present study, a temperature- and pH-stable laccase was purified from the spores of Bacillus ballismortis fmb-103 and was used to degrade malachite green. The laccase from fmb-103 (fmb-L103) was purified 15.2-fold to homogeneity (389.9 mU/mg protein with respect to ABTS as a substrate) by precipitation with 30-80% (NH4)2SO4, DEAE-Sephadex A-50 ion exchange chromatography, and Sephadex G-100 chromatography. fmb-L103 is a nonblue laccase with a molecular weight of 55.0 kDa and Cu content of 2.5 (mol:mol). fmb-L103 retained more than 50% activity after 10 h at 70 °C and demonstrated broad pH stability in both acidic and alkaline conditions. The effects of inhibitors and metal ions on fmb-L103 activity were also examined. A kinetic study revealed that ABTS was a suitable substrate with a Km of 22.7 μmol and a Vmax of 3.32 μmol/mL/min. fmb-L103 can efficiently degrade malachite green after a 48 h treatment period in combination with a mediator, without the appearance of leucomalachite green.