<p>Landfills, serving as the primary disposal sites for municipal solid waste, are increasingly recognized for their potential to contribute to arsenic (As) contamination. The As toxicity and mobility are closely associated with its chemical speciation, with inorganic As species—arsenate [As(V)] and arsenite [As(III)]—being the most prevalent and problematic. The transformation of these species poses substantial risks to both ecosystems and human health. This study delves into the biomineralization behaviors of As(V) and As(III) under the influence of sulfate-reducing bacteria (SRB) isolated from refuse. Results indicate that SRB facilitate the dissimilatory sulfate (SO₄²⁻) reduction process, converting SO₄²⁻ to hydrogen sulfide (H₂S)/hydrosulfide (HS⁻), which subsequently reacts with As(III) to form insoluble arsenic-sulfide minerals like As₂S₃, AsS, and As₄S₄. As(III) demonstrated a superior biomineralization potential, with mineralization rates reaching 16.09% (T3) and 20.43% (T4) in As(III)-amended reactors, significantly exceeding those in As(V)-amended reactors (T1 and T2). X-ray diffraction and scanning electron microscopy analyses confirmed the predominant formation of AsS in the presence of As(III) reactor, while As(V) reactor contributed to the formation of As₄S₄. Both environmental parameters, such as pH and SO₄²⁻ concentration, and the microbial community composition critically influenced the As biomineralization behaviors. Metagenomic sequencing uncovered the pivotal roles of SRB and As(V)-reducing bacteria, including <i>Clostridium</i> and <i>Desulfitobacterium</i>, in mediating SO₄²⁻ reduction and the detoxification of As(V). This research offers novel insights into the biomineralization mechanisms of As within landfills and lays a theoretical groundwork for the remediation of As pollution.</p>