Abstract: The cytological characters of Sinojackia xylocarpa Hu in mitosis and meiosis were investigated. Its karyotype could be formulated as 2n=2x=24=4 m+7 sm(2SAT)+1 st,belonging to Stebbins's 2A type.The mitotic resting nucleus showed the complex chromocentre type,and at prophase there were B-chromosomes existed.The chromosomes were moderate size.At meiotic metaphase the configurations of 12 pairs of bivalents were almost common,while at anaphase I and anaphase II occurred various kinds of abnormality of chromosomal behaviour including fragment,lagging chromosome or chromosomal bridge.Statistic data showed that there was a relatively congruent occurrence between the abnormal chromosome proportion and the abortive pollen proportion,it seemed to reveal that there were some cytological factors companied with the higher pollen sterility and lower seed germination of S.xylocarpa However,the further research based on molecular genetics and pollination biology to the endangered mechanism of S.xylocarpa remained to be done.