Arginase (Arg) is an enzyme that catalyzes the degradation of arginine to produce urea and omithine, which is crucial in the urea cycle. In most mammals, two isozymes of this enzyme exist; the first, Arginase I, functions in the urea cycle, and is located primarily in the cytoplasm of the liver. The second isozyme, Arginase II, has been implicated in the regulation of the arginine/ornithine concentrations in the cell. Besides, Estrogen Receptor Alpha (ERa) has been identified as an interactor of, thus a binding ELISA assay was conducted to detect the interaction of recombinant rat Arginase( Arg) and recombinant rat ERa. Briefly, Arg were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100uL were then transferred to ERa-coated microtiter wells and incubated for 2h at 37℃. Wells were washed with PBST and incubated for 1h with anti-Arg pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody, wells were aspirated and washed 3 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50µL stop solution to the wells and read at 450nm immediately. The binding activity of of Arg and ERa was shown in Figure 1, and this effect was in a dose dependent manner.