Abstract: The process of floral-bud differentiation in Osmanthus fragrans ‘Dangui’ and O. fragrans ‘Ziyingui’ was studied by the paraffin method. The process can be divided into 6 stages of differentiation: early, involucrum, single flower, perianth, androecium, and gynoecium. ‘Ziyingui’ and ‘Dangui’ do not differ in androecium development; stamens can develop into normal pollen sacs and ripe pollens. However, the fertile ‘Ziyingui’ and sterile ‘Dangui’ do differ in gynoecium development. Floral-bud differentiation study suggests that the abnormal pistil development of ‘Dangui’ leads to its sterility.