Influenza A and B viruses and some paramyxoviruses contain sialidases that hydrolyze terminal sialic acid (viral receptor) from glycans. Cells infected with these viruses express high levels of viral sialidase derived from the viral genome. The sialidase imaging probe developed in our study histochemically visualizes the location of sialidase activity. The probe is a water-soluble and non-fluorescent compound that incorporates sialic acid into a hydrophobic fluorescent compound, (2-benzothiazol-2-yl)-4-bromophenol. The probe enables easy and rapid fluorescence imaging of infected cells expressing viral sialidases without using antiviral antibodies and cell fixation reagents. The probe is applicable to virus isolation and detection for drug-resistant influenza virus against sialidase inhibitors of anti-influenza drugs. In addition, we have developed a new sialidase imaging probe more suitable for the accurate imaging of sialidase localization. In this review, we have introduced our work on sialidase imaging probes that visualize viral sialidases.