Purpose Epithelial-to-mesenchymal transition (EMT) is a phenotype that alters cell morphology, disrupts morphogenesis, and increases motility. Our prior studies have shown that the progeny of human mammary epithelial cells (HMECs) irradiated with 2 Gy undergoes transforming growth factor β (TGF-β)–mediated EMT. In this study we determined whether radiation dose or quality affected TGF-β–mediated EMT. Methods and Materials HMECs were cultured on tissue culture plastic or in Matrigel (BD Biosciences, San Jose, CA) and exposed to low or high linear energy transfer (LET) and TGF-β (400 pg/mL). Image analysis was used to measure membrane-associated E-cadherin, a marker of functional epithelia, or fibronectin, a product of mesenchymal cells, as a function of radiation dose and quality. Results E-cadherin was reduced in TGF-β–treated cells irradiated with low-LET radiation doses between 0.03 and 2 Gy compared with untreated, unirradiated cells or TGF-β treatment alone. The radiation quality dependence of TGF-β–mediated EMT was determined by use of 1 GeV/amu (gigaelectron volt / atomic mass unit) 56Fe ion particles at the National Aeronautics and Space Administration’s Space Radiation Laboratory. On the basis of the relative biological effectiveness of 2 for 56Fe ion particles’ clonogenic survival, TGF-β–treated HMECs were irradiated with equitoxic 1-Gy 56Fe ion or 2-Gy 137Cs radiation in monolayer. Furthermore, TGF-β–treated HMECs irradiated with either high- or low-LET radiation exhibited similar loss of E-cadherin and gain of fibronectin and resulted in similar large, poorly organized colonies when embedded in Matrigel. Moreover, the progeny of HMECs exposed to different fluences of 56Fe ion underwent TGF-β–mediated EMT even when only one-third of the cells were directly traversed by the particle. Conclusions Thus TGF-β–mediated EMT, like other non-targeted radiation effects, is neither radiation dose nor quality dependent at the doses examined.