Intracellular phosphate (Pi) is normally maintained at a fairly constant concentration in Escherichia coli, mainly by Pi transport systems and by the ‘phosphate balance’ between Pi and polyphosphate (polyP). We have reported previously that excess uptake of Pi in a phoU mutant results in elevated levels of polyP. Here, we found that the elevated levels of polyP in the mutant could be reduced by the overproduction of YjbB, whose N-terminal half contains Na+/Pi cotransporter domains. The rate of Pi export increased when the YjbB overproducer grew on a medium containing glycerol-3-phosphate. These results strongly suggested that YjbB reduced the elevated levels of polyP in the phoU mutant by exporting intracellular excess Pi.