One of the male sterile traits in citrus is the interruption of anther development. It has been known that hybrids with undeveloped anthers segregate among hybrids with satsuma mandarin. In this study, the mode of inheritance of undeveloped anthers was studied using 'Kiyomi' (C. unshiu×C. sinensis) and 20 citrus cultivars and strains. 'Kiyomi' is a superior commercial variety with cytoplasm identical to the satsuma mandarin. Although undeveloped anthers in citrus are designated as cytoplasmic-genic male sterility, it was possible to study the nuclear genes only by using 'Kiyomi' as a seed parent in all cross combinations. When three strains that are progenies of 'Kiyomi' were backcrossed with 'Kiyomi', the ratios of undeveloped anthers to developed anthers in their progenies were 1 : 7 or 1 : 3, indicating that the undeveloped anther is related to three pairs of homomeric nuclear genes AD1, AD2, and AD3. The genotype of 'Kiyomi' with an undeveloped anther is supposed to be ad1ad1ad2ad2ad3ad3, according to this hypothesis, which is supported by the segregation ratios in the progenies from 12 other cross combinations. However, when 'Kiyomi' was crossed with three satsuma mandarins, most of the progenies produced undeveloped anthers which reveal that this anomaly in citrus is controlled by more than three homomeric genes. Because satsuma mandarin and 'Kiyomi' have accumulated these genes, these cultivars are very important for the breeding of seedless citrus.