A microcosm mimicking artificial groundwater harboring high (75 mM) AS(III) concentration was developed to study the rate of arsenic oxidation by Bacillus sp. L-148 under different conditions. Na. acetate and glucose as carbon sources were used along with and/or absence of Fe ions. Morphological studies revealed elongation of 75 mM As(III) exposed bacteria along with terminal spore formation. Decrease in pH with time and As(V) formation was seen. Maximum 77% oxidation in presence of Na. acetate and Fe ions on 15th day was seen. Growth studies were in analogy with As oxidation studies. Microcosm for As oxidation in presence of 0.4 mM mixture of heavy metals Cd, Co, Pb, Li, As(III), As(V), Sb was studied. Effect of heavy metals on growth and As(III) oxidation was assessed. Contrastingly, here glucose served as a better carbon source but completely oxidized As(III). Thus, this microcosm study concluded that Bacillus sp. L-148 can be used for bioremediation of heavy arsenic contaminated site along with presence of other heavy metals.