Agrobacterium-mediated transformation and particle bombardment are two gene delivery systems that have been widely used in plant genetic transformation. The introduction of green fluorescent protein (GFP) gene and its detection system to plant genetic transformation has ameliorated the lack of suitable marker genes needed to study transgenic gene expression in different cell lines, in different stages of plant development, and in different organs of plant. Here we report our studies on temporal and spatial expression of GFP gene in transgenic cotton. Our results showed that GFP expression was (i) different in different cell lines, (ii) effected by embryogenic status of cell, (iii) altered by increased chlorophyll content as the transgenic embryo develops, and (iv) different between plant organs.