Objective Study on the absorption, distribution, transformation, excretion and toxicity of four forms of arsenic in rats. Methods Four thousand and fifty data were obtained from 28 days animal metabolism experiments of 81 rats exposed to the four As species. Distribution, metabolism, excretion, and subacute toxicity of 4 As species were compared by analyzing the arsenate [As(V)], arsenite [As(III)], methyl arsenate (MMAV) and dimethyl arsenate (DMAV) content of rat feces (excrement and urine), blood, seven organs, and liver and kidney pathology. Results After oral administration of each As species, 82.9% of As(III), 85.1% of As(V), 95.0% of MMAV and 96.2% of DMAV were accumulatively secreted via feces and urine, while 16.2% of As(III), 14.1% of As(V), 4.65% of MMAV and 0.120% of DMAV were detected in blood. The DMAV accumulated in blood and urine after dosing As(III), As(V) and MMAV, and the content of DMAV in the blood was 8 times greater than urine. Four kinds of arsenic had effects on rat liver and kidney function, the influence on liver was acute phase effect while that on renal was cumulative effects. The effect of As(III) was the most significant, followed by MMAV. Four kinds of arsenic could cause tissue deformation and inflammatory cells infiltration, but showed no difference between groups. Conclusion The distribution, metabolism, excretion, and toxicity of the four kinds of arsenic in rats were different in varying degrees. The research of health risk for arsenic should consider its different forms.