Gold nanoparticles (GNPs) have considerable applications in biomedicine, such as in bio-sensing, bio-imaging, drug delivery and photothermal therapeutics. However, currently there are limited information regarding the impact of pregnancy on their biodistribution, elimination and toxicity. In this study, we investigated the biodistribution and potential toxic effects of different-sized GNPs (1.5, 4.5, 13, 30 and 70. nm in diameter) in non-pregnant and pregnant mice at different gestational ages (E5.5, 7.5, 9.5, 11.5 and 13.5). 5. h after intravenous injection, GNPs exhibited size-dependent biodistribution profiles; however, regardless of size, no significant biodistribution changes were observed between non-pregnant and pregnant mice. Kinetic studies showed that 4.5. nm GNPs were primarily excreted through urine within 5. h, whereas 30. nm GNPs had a more prolonged blood circulation time. No apparent toxic effects (e.g., increased mortality, altered behavior, reduced animal weight, abnormal organ morphology or reduced pregnancy duration) were observed with different-sized GNPs in pregnant mice. However, treatment with 30. nm GNPs induced mild emphysema-like changes in lungs of pregnant mice. These results indicated that the maternal biodistribution patterns of GNPs in pregnant mice depended on particle size, but not gestational age organ-specific adverse effects may arise with treatment with some GNPs according to their size. © 2014 Elsevier Ireland Ltd.