Abstract: Genomic in situ hybridization (GISH) technique was established in Citrus to identify intergeneric sexual hybrid. It showed that the modified procedures could be further used to identify Citrus somatic hybrids. Flame-drying protocol after enzyme digestion of cell wall was a good method for getting clear and well dispersed Citrus chromosome preparation with few debris. With probe DNA labeled by nick translation, and the blocking DNA being 50 times the amount of the probe DNA, Carrizo citrange,an intergeneric sexual hybrid of Citrus, was successfully identified by GISH method.