Since CdSe nanoplatelets were reported to have a ten-fold higher two-photon (2P) absorption coefficient as compared to quantum dots, we examined their applicability for cell labeling and 2P imaging. CdSSe/ZnCdS core-shell nanoplatelets and CdSe/ZnS quantum dots, both emitting at 585 nm were encapsulated with an amphiphilic zwitterionic polymer having slightly positive zeta potential. As measured with flow cytometry, glioma C6 cells demonstrated equally efficient uptake of nanoplatelets and quantum dots, despite the different sizes of these two types of nanoparticles. 2P fluorescence microscopy revealed ca. two orders of magnitude higher fluorescence response from nanoplatelets thus offering a chance to use them as highly efficient 2P fluorescent labels in biomedicine.