The need to monitor and verify the presence and the amount of genetically modified organisms (GMOs) in agricultural crops and in products derived thereof has generated a demand for analytical methods capable of detecting, identifying and quantifying either the DNA introduced or the protein(s) expressed in transgenic plants, because these components are considered as the fundamental constituents. The specific detection of a novel protein synthesized by a gene introduced during transformation constitutes an alternative approach for the identification of genetically modified plants. One of the most studied proteins, which is the result of expression of marker gene, is Green Fluorescent Protein (GFP), isolated from Aequorea victoria. This protein is largely used as fluorescent marker of gene expression in bacteria, plants and animals. The protein absorbs ultraviolet light from the sunlight, and then emits it as lower-energy green light. Main advantage of this marker gene is the lack of substrate or special conditions for material fixing in purpose to evidence its functionality. Native or recombinant protein is 27 kDa and contains 238 amino acids. Our research was held on two species of non-modified plants (tobacco Doina, tomato Fakel, Republic of Moldova) and four genotypes (tobacco TM-1, tobacco TM-2, tomato and Arabidopsis thaliana, UCR, USA). Transgenic plants were modified with the pCAMBIA 3301 vector. This plasmid in tobacco contained hygromicine gene, gfp gene and gus gene; in Arabidopsis thaliana - npt II gene, NOS terminator and CaMV 35 S sequences; in tomato - npt II, gus genes, 35S CaMV and NOS-terminator sequences. For GFP identification electrophoresis of total proteins was done. Gfp gene expression was determined by detection of specific 27 kDa band in the electrophoresis gel. Thus, comparison of the three forms of tobacco the specific band was revealed at transgenic plants, TM-1 and TM-2, and was absent at other genotypes.