<p>Cadmium (Cd) and arsenic (As) co-contamination in paddy soils may lead to their accumulation in rice grains, creating health concerns for humans. While iron (Fe) nutrition has emerged as a promising mitigation strategy, the impact of application timing is not well understood. This study evaluated the effects of chelated iron (EDTA·Na₂Fe) applications at two growth-stage combinations: pre-transplanting + booting and tillering + booting. Both treatments reduced Cd and As concentrations in rice grains; however, the tillering + booting treatment was the more effective, decreasing grain Cd and As levels by 53.2% and 60.7%, respectively. This reduction is linked to decreased Cd (9.6%–29.9%) and As (10.7%–15.3%) soil availability, and restricted translocation within the plant. The tillering + booting treatment specifically limited soil Cd bioavailability and root-to-grain Cd transport, and inhibited As transfer from iron plaques to roots and from vegetative tissues to grains. These findings demonstrate that stage-targeted application of EDTA·Na₂Fe, particularly during the tillering and booting stages, is an effective agronomic strategy for minimizing Cd and As accumulation in rice cultivated on co-contaminated soils.</p>