In this paper, we report a generalized functionalisation strategy, which enables conjugation of lectin to a gold nanoparticle (GNP) surface without affecting the lectin properties. The lectin-GNP conjugates are prepared by coupling lectins to the GNP surfaces through a bifunctional linker PEG NHS ester disulfide (NHS-PEG-S-S-PEG-NHS). Subsequently, additional PEG-thiol (mPEG-SH) ligand is applied to the GNP suspension in order to block nonspecific adsorption sites on the GNP surface and improve the stability of the lectin-GNP conjugate. The interactions of six lectin-GNP conjugates with six cell lines have been visualized by conventional microscopy and semi-quantitatively analyzed by the UV-visible spectroscopic technique, respectively. The experimental results demonstrate that the lectin-GNP conjugates can bind to living cells with high efficiency and have a great promise to be used as optical probes for monitoring specific affinities of cells with lectins, and evaluating glycosyl complexes on living cell surfaces.