Abstract: Using different mutants of green fluorescent protein (GFP) as the donor and acceptor for FRET pair, and both the donor and acceptor are fused to two different host proteins or at two different sites within the same protein molecular biology technique, one can monitoring the dynamical protein-protein interaction in real-time in single living cell. This paper presents the application of FRET based on the GFPs in the study of dynamics of biological molecules in single living cell.