The potential utility of mesophilic/moderately thermophilic acidophiles was investigated for immobilization of arsenic (As) as scorodite (FeAsO4·2H2O) at moderate temperatures (35–45˚C). Here, the acid-tolerant mesophile Thiomonas cuprina Hö5 and acidophilic moderately thermophile Acidimicrobium ferrooxidans ICP were selected as As(III)- and Fe(II)- oxidizers, respectively. Due to a difference in their optimal growth pHs, a 2-step reaction consisting of the 1st As(III) oxidation step followed by the Fe(II) oxidation + precipitation step was studied. In our previous study, the optimal [Fe(II)]ini/[As(III)]ini molar ratio for bioscorodite formation at 70˚C (at [As(III)]ini = 1000 ppm) was shown to be around 1.4. However, setting the same molar ratio at moderate temperatures (35-45˚C) resulted in formation of unstable amorphous ferric arsenate. Lowering the ratio to ≤ 1.0 led to precipitation of crystalline bioscorodite with > 90% As(III) removal at 45˚C.