Gastrointestinal symptoms, including nausea and vomiting, are common adverse effects of oral iron tablets, but the mechanism of iron-induced nausea and vomiting is not yet known. Studies have shown that there are close relationships between gastrointestinal motility and gastrointestinal symptoms such as nausea, vomiting, and diarrhea, with more than 90% of patients with delayed gastric emptying experiencing nausea and vomiting. However, the effect of iron on gastrointestinal motility has not yet been investigated. In the present study, we aimed to elucidate the effects of iron on gastrointestinal motility using sodium ferrous citrate (SFC),  the most commonly used iron tablets. Gastric emptying in mice was assessed by ¹³C-octanoic acid breath test to examine the effect of SFC (3-30 mg Fe/kg, p.o.) with or without the 5-HT₃ receptor antagonist, palonosetron hydrochloride (5 mg/kg. s.c.). Colon transit was also measured by the beads method. The results showed that SFC delayed the gastric emptying, which was ameliorated by administration of palonosetron hydrochloride. It was also confirmed that ingredients of the tablets had no effect on gastric emptying. SFC also had no effect on the colon transit in vivo. These results lead the possibility that the iron-induced delayed gastric emptying may be mediated through nausea and vomiting.