New amphiphilic near-infrared fluorescent probes (λem = 710 nm) are reported for monitoring viscosity of cell membranes. The probes were found to be selective and sensitive to viscosity, and to quickly (within 2 minutes) and stably anchor onto the cell membrane. Moreover, the applicability of the probe MYN-BS (a superior representative) was demonstrated, revealing a reversible viscosity change with temperature change and an increase in viscosity during cell foaming. The proposed probes may serve as a reliable tool for studying viscosity-related processes of cell membranes.