In this study, a strain with strong ability to decolorize and degrade malachite green was isolated from a malachite green-contaminated aquaculture pond by the color-changing zone method. By 16S rDNA sequence alignment and phylogenetic tree analysis, as well as using the microbial identification system VITEK 2, the strain was identified as Klebsiella pneumoniae and named as WA-1. The effects of different carbon sources on decolorization and degradation of malachite green by WA-1 were studied by spectrophotometry and KBH₄ reduction-high performance liquid chromatography with fluorescence detection (HPLC-FLD). The results showed that this strain potently decolorized and degraded malachite green in the salt medium. The decolorization rate of malachite green at 5-40 mg/L was increased to approximately 100% after the addition of carbon sources including glucose, galactose, and sucrose, while the degradation rate was significantly reduced, especially at 5 mg/L. Malachite green was reduced to leucomalachite green by malachite green reductase outside the cells, which could enter the cells through active transport for decolorization and degradation. The mechanism of the effect of different carbon sources on the decolorization and degradation of malachite green was also revealed. The results of this study provide an important idea to reveal the mechanism of malachite green degradation by K. pneumoniae WA-1, and also provide an important theoretical basis for the application of malachite green degradation in the future.