Rice (Oryza sativa) is a major dietary source of arsenic (As) for the population consuming rice as their staple food. Rice grain contains both inorganic As and methylated As species, especially dimethyarsinate (DMA). DMA is highly mobile in long-distance translocation in plants, but the underlying mechanism remains unknown. In the present study, we showed that OsPTR7 (OsNPF8.1), a putative peptide transporter in rice, was permeable to DMA in Xenopus laevis oocytes. Transient expression of the OsPTR7-green fluorescent protein (GFP) in tobacco protoplasts showed that OsPTR7 was localized in the cell plasma membrane. Quantitative real-time PCR analysis showed that OsPTR7 was more highly expressed in the shoots than in the roots at the seedling stage. At the flowering and grain-filling stage, the OsPTR7 transcript was abundant in the leaves, node I and roots. Knockout or knockdown mutants of OsPTR7 had significantly decreased root to shoot translocation of DMA compared with wild-type plants and accumulated less As in the brown rice. In field-grown plants, DMA accounted for 35% of the total As in the brown rice of wild-type plants but was undetectable in the knockout mutant. Our study demonstrates that OsPTR7 is involved in the long-distance translocation of DMA and contributes to the accumulation of DMA in rice grain.