The study aims to clarify the differential gene expression between cotton hybrids and their parents in order to better understand the molecular basis of cotton heterosis. The research focused on cotton heterotic and lower heterotic hybrids and their parents during the four crucial stages, which were analyzed using a differential display technique. The results indicated that there were both quantitative and qualitative differences in gene expression amongst them. The quantitative differences include over- and under-expression of parental genes and the dominant expression of highly-expressed parental genes in hybrids. In contrast, the qualitative differences are the following: (i) Bands were observed in both parents but not in the F1 hybrid (BPnF1); (ii) bands occurred in either of the parents but not in the F1 hybrid (UPnF1); (iii) bands presented only in the F1 hybrid but not in either of the parents (UF1nP); and (iv) bands were detected in either of the parents and the F1 hybrid (UPF1). Overall, the major differences of gene expression occurred in the qualitative level and four related differential patterns were observed. Furthermore, the amount of differential patterns during the flowering stage was relatively higher than those of other stages. At this juncture, both the amount of hybrid-specific expression patterns at flowering stage and the silenced expression patterns at boll-forming stage in highly heterotic hybrids were found higher than those in the lower heterotic ones. It was concluded that significant differences of gene expression in leaves were present between cotton hybrid and its parents during the whole growing stages. Hence, these differences might be responsible for the observed cotton heterosis. The study aims to clarify the differential gene expression between cotton hybrids and their parents in order to better understand the molecular basis of cotton heterosis. Which research focused on cotton heterotic and lower heterotic hybrids and their parents during the four crucial stages, which were analyzed using The results indicated that there were both quantitative and qualitative differences in gene expression amongst them. The quantitative differences include over- and under-expression of parental genes and the dominant expression of highly-expressed parental genes in hybrids. In contrast , the qualitative differences are the following: (i) Bands were observed in both parents but not in F1 hybrids (BPnF1); (ii) bands occurred in either of the parents but not in F1 hybrids (UPnF1); (iii) bands presented only in the F1 hybrid but not in either of the parents (UF1nP); and (iv) bands were detected in either of the parents and the F1 hybrid (UPF1 ), Overall, the major differences of gene expression occurred in the qualitative level and four related differential patterns were observed. Furthermore, the amount of differential patterns during the flowering stage was relatively higher than those of other stages. At this juncture, both the amount of hybrid-specific expression patterns at flowering stage and the silenced expression patterns at boll-forming stage in highly heterotic hybrids were higher than those in the lower heterotic ones. It was concluded that significant differences of gene expression in leaves were present between cotton hybrids and its parents during the whole growing stages. Therefore, these differences might be responsible for the observed cotton heterosis.