G-quadruplexes (G4s), non-canonical nucleic acid secondary structure,r egulate many biological functions and are considered potential molecular targets for cancer therapeutics.H owever,d ue to the lacko fa nalytical methods,t he regulating mechanism of monogenic G4s is still unclear.Here, we developed aM odule Assembled Multifunctional Probes Assay (MAMPA) for visualizing endogenous G4s in individual genes in single cells.T wo modular probes separately recognizeG4structures and the adjacent RNAsequences,and the module assembly enables imaging of G4s in an individual RNAw ith high specificity.T hrough imaging G4s in several individual genes,wefound that G4s were steadily occupied by G4 Binding Proteins (G4BPs) in various mRNAs in every cell line and defined "Occupied G4 Ratio". We demonstrated MAMPAw as suitable for most experimental situations and found that Occupied G4 Ratios had the potential to become anew parameter for the study of G4s in living cells.