Abstract: In order to verify the hybrid incompatibilities among different hybrids groups belonging to Rhododendron Subgenus Hymenanthes，302 hand cross pollination treatments among 33 cultivars were conducted. According to a previous cultivar classification，all these hybrids can be divided into the Griffithianum hybrids group（Gr），Fortunei hybrids group（F），Gatawba hybrids group（Ga），Caucasicum hybrids group（C）and Degronianum hybrids group（D），respectively. The fruit set，seed set and seed germination rate were then statistically analyzed. Moreover，another types of cross pollinations including two hybrid groups as male and all these 5 different hybrids groups as female were conducted. The pollen germination rate，the pollen length/style length and the rate of the fertilized ovules in the crosses were observed by the fluorescence microscopy. The results showed that：（1）Fruit sets were varied when the same cultivar was used as the different parents. In 33 cultivars，11 cultivars were suitable as female and 5 cultivars were suitable as male，whereas 16 cultivars could be used as both female and male，however 1 cultivar‘Cosmopolitan’was not suitable as parents；With regards to the 5 hybrids groups，Gr was suitable as female，F was suitable as male，and Ga could be used as both，and the fertilization effect of C and D was related to its matching. The unilateral sterility，the bilateral fertility or sterility could be found among these different hybrids groups.（2）The order of the fruit set，seed set and the seed germination rate of the 5 hybrids groups as female parent were Ga > Gr > C > D > F，Ga > C > Gr > D > F，Ga > C > F > Gr > D，respectively；and the order of the fruit set, seed set and the seed germination rate of the 5 hybrids groups as male parent were F > Ga > Gr > D > C，F > Ga > D > C > Gr，F > Ga > Gr > C > D，and the order of the fruit set，seed set and the seed germination rate of the 5 hybrids groups as parent were Ga > F > Gr > D > C，Ga > F > D > C > Gr，F > Ga > C > Gr > D.（3）According to the pollen fluorescence microscopic observation，the pollen grains of all the tested crosses could germinate except the pollination treatment of D × F. However，the pollen tube length/style length of the cross combinations were different，and their fertilized ovule rate were low. In summary，there were obvious infertility phenomena among the different hybrids groups of Rhododendron Subgenus Hymenanthes，and the sterile types included no fruits，no seeds or no seed germination，and the pre-fertilization and post-fertilization barriers could contribute to these different types of incompatibilities.

Key words: Rhododendron Subgenus Hymenanthes, hybrids group, cross compatibility, setting capsules rate, seed germination rate；pollen, fluorescence microscope observation