Glycosylation is one of the most important posttranslational modifications of proteins. In addition to cell-surface proteins, many intracellular proteins, such as cytoplasmic, nuclear and mitochondrial proteins, are also glycosylated. The intracellular glycosylation processes are adjusted by different functionally specific glycosyltransferases and glycosidases. Among the various intracellular glycosylation processes, O-GlcNAcylation and sialylation are two main types that play critical roles in the regulation of the structure, function and localization of proteins. Hence visualization of intracellular glycosylation is of great importance for revealing glycosylation-related biological processes. Owing to the complicated intracellular environment, visualization of intracellular glycosylation processes is a great challenge. By utilizing glycan labelling methods and glycol–enzyme-induced fluorescence resonance energy transfer (FRET) or competitive binding, preliminary visualization of intracellular O-GlcNAcylation- and sialylation-related enzyme activities has been achieved. This chapter presents a detailed description of current methods developed for the visualization of intracellular glycosylation, including the design and preparation of glycan-recognizable probes, protein labelling and signal switches. Future developments should be focused on the fabrication of biomimetic molecular probes with novel recognition mechanisms and the glycosylation events in specific organelles require more investigation.