The oral ingestion of ZnO nanoparticles (NPs) has attracted considerable attention because of the wide usage in food packaging and additives. The small intestine is the major absorption site for ZnO NPs. Unfortunately, studies on the absorption of ZnO NPs in the GIT were still scarce. This study evaluated the absorption characteristics of ZnO NPs (30 nm) and bulk ZnO (rod morphology with a mean size of 139 846 nm). Results showed that ZnO NPs and bulk ZnO were absorbed and redistributed in various organs of mice at 4 h after exposure. Significantly higher levels of MT1 were observed in the duodenums of bulk ZnO and ZnO NPs groups than those of the control (9.8 and 5660.11 fold increases, respectively). The MT4 levels in the bulk ZnO and ZnO NPs groups also showed 4.07 and 43.21fold increases, respectively. In addition, the transcript levels of Zips, ZnTs, and MTs in the jejunum of bulk ZnO group were higher than those of ZnO NPs group. And the transcript levels of ZIPs, ZnTs, and MTs were all lower in the ileum than in the jejunum. The results suggested that ZnO NPs were mainly absorbed in the duodenum in the form of particles and can be absorbed as Zn2+ in the jejunum and secondly in the ileum. By contrast, bulk ZnO was more easily absorbed as Zn2+ in the jejunum and secondly in the ileum. (C) 2017 Elsevier Inc. All rights reserved.