Abstract:Catalpa bungei C.A.Meyer, a deciduous tree belonged to Catalpa Bignoniaceae, is a unique timer tree species with high quality and value in China. Paraffin sectioning with optical microscopy was conducted to investigate the development of megasporogenesis, microsporogenesis and the developing process of female and male gametophytes in fertile and sterile lines of C.bungei flowers. The development of pistil in fertile plants and sterile plants were basically the same, including anatropous ovule with simple integument and tenuinucellus, and polygonum type embryo sac. The anther of fertile plants was tetrasporangiate and anther connective parenchyma was well-developed. The heterotype tapetum consisted of anther wall tapetum and anther connective tapetum. Before the meiosis of microspore mother cell, the epidermal cells of anther wal began to elongate and thicken radially without degradation till anther cracking, which might be related to anther cracking. The matured pollen of fertile plants were tetrasomic. The anther development of sterile plants in early secondary sporogeous cells stage was almost the same with fertile stamen. The tapetum developed incompletely during the meiosis period of microspore mother cells. The tapetum cells were highly vacuolated with thin cytoplasm and prematurely degraded during the tetrad stage, and the tetrad microspore developed abnormally due to structural and functional abnormity of tapetum. Therefore, the male sterility of C.bungei was structural type male sterility.