Flooded rice cultivation significantly promotes arsenic (As) methylation and volatilization in soils. Dimethylarsenate (DMAs) as the main product of As methylation can cause straighthead disease symptoms in rice plants. Notably, DMAs in rice is formed by microbes present in the soil as rice plants themselves cannot methylate arsenite (As(III)). Moreover, although dissolved organic matter (DOM) can change As activity and speciation in soils, whether DOM can affect As methylation and volatilization in paddy soils, and the performance of DOM with different origins remains unclear. In this study, we prepared DOM from different sources such as pig manure, cow dung, chicken manure, and rice straw and characterized their elemental composition and functional groups. The methyl As content in soil solution and the trapped volatile As from paddy soils following DOM application were analyzed. The abundance and community structure of the total bacteria and functional bacteria encoding arsenite S-adenosylmethionine methyltransferase (arsM) were observed using Illumina high-throughput sequencing. The results showed that pig manure and rice straw DOM exhibited the highest and lowest ability to methylate As with an efficiency of 18.6 and 10.0 µg methyl As g⁻¹ total organic content in paddy soil, respectively. Based on the volatile As trapping device, the trapped As in paddy soils following pig manure DOM application was approximately 2.7- and 9.6-fold higher than that of soils treated with rice straw DOM and the control after 13 weeks of incubation, respectively. Specifically, trimethylarsenate, accounting for 54%, represented the highest trapped As species in silica beads. The copy number of the total and arsM bacteria was significantly enhanced in paddy soils treated with DOM. arsM copy number and methyl As content in paddy soils were significantly positively correlated (P < 0.01). Bacterial strains such as Proteobacteria, Bacteroidetes, Geobacter, Sphingomonas, Streptomyces, and Rhodopseudomonas capable of As reduction, methylation, or volatilization emerged largely in paddy soils following pig manure DOM addition. Additionally, numerous carboxyl (-COOH) groups were observed in the pig manure DOM, which facilitate the desorption of inorganic As from the soil colloid and increase of As methylation substrate. The relative abundance of aliphatic compounds with non-polar alkyl C and N-alkyl C functional groups in pig manure DOM supports the bacterial growth in paddy soils, as opposed to rice straw DOM that contains more aromatic compounds with aromatic C-O. In conclusion, DOM presenting different physicochemical characteristics can differentially promote As methylation and volatilization in paddy soils by changing the As methylation substrate and the abundance and community structure of arsM bacteria. These observations will provide a better understanding of DOM-mediated promotion of As methylation and volatilization in paddy soils.