Here we report carboxy-eosin as a fluorescent marker for in vivo visualization of DNA in the correlative (fluorescence and electron) biological microscope. For that purpose a fluorescent thymidine analog 2’,4’,5’,7’-tetrabromofluorescein-aminoallyl-dUTP (eosin-aminoallyl-dUTP) was synthesized and incorporated into the genome of Escherichia coli. The fluorescent dye eosin contains four bromine atoms, which enable electron spectroscopic imaging in the transmission electron microscope. Labeled cells were prepared and directly observed by fluorescence and electron microscope without any preliminary fixation step. We demonstrated that eosin-aminoallyl-dUTP is a suitable marker for imaging of cell’s ultrastructures by correlative biological microscopy.