Potential occupational As exposure is a significant problem in smelting plants. The metabolites containing As with an oxidation of +3 were considered more cytotoxic and genotoxic than their parent inorganic species. The current study examined the capacity of As methylation and its risk on skin lesions. The primary aim of this study is to determine if methylation capacity, as measured by urinary As metabolites, differed in workers with skin lesions compared to workers without skin lesions. Hydride generation-atomic absorption spectrometry was used to determine 3 As species in urine of workers who had been working in As plants, and primary and secondary methylation indexes were calculated. Skin lesions were examined at the same time. Many workers had obvious skin lesions (36/91). The mean concentrations of inorganic As (iAs), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in the urine of workers are obviously higher than those of the control group. There are more iAs, MMA, and DMA in urine, higher MMA%, lower iAs% for workers with skin lesions compared with those without skin lesions. Workers with skin lesions have the lowest SMI (3.50 ( 1.21), and they may be in danger. The authors concluded that the findings from this study support the viewpoint that individuals who metabolise inorganic As to MMA easily, but metabolise MMA to DMA difficulty have more risk of skin lesions.