Abstract: Green fluorescent protein (GFP) from the jelleyfish Aequorea victoria is responsible for the bioluminescence. The Aequrea GFP is composed of 238-aa-residue with a calculated Mr of 26888D. The highly fluorescent chromophore is composed of a modification of the Ser-Tyr-Gly at positions 65~67 within the polypeptide. These three residues are cyclized and oxidized to form the phydroxybenzylidene-imidazo-lidinone chromophore. The expression of wild-type GFP in stably transformed plants has typically yielded very faint or no green fluorescence. The engineered GFP gene was resynthesized to adapt its codon usage for expression in plant by increasing G or C content to mutate the cryptic intron for escaping the aberrant mRNA processing. The modified GFP versions were used as a reporter gene in place of GUS gene, as a marker gene and as a subcellular targeting tool in plant. In addition, GFP was effective in the research of ecological monitoring and interactions between microbes and plants.