Abstract: The main reason for pollen abortion in Aloe arboresens Mill. was studied through the observation of meiosis and the microspore development of its pollen mother cells(PMCs). There are 14 chromosomes in the PMC of Aloe arboresens Mill., containing four pairs of long chromosomes and three pairs of short ones, and this karyotype belongs to dichotocarpism. Abnormalities observed were fallen into four categories:(1) Univalents, they were caused by failure in pairing, asynapsis and precocious cancellation of terminal chiasma. Oriented univalent pair was distributed at two poles normally in anaphase, while non-oriented univalent pair only at one pole. Another factor leading to univalents was that chromosomes were paired but without substantial exchange. (2) Multivalents. They might be produced by translocation heterozygote.(3) Chromosome bridges. There were three kinds of bridges in anaphaseⅠand anaphaseⅡ: single and double chromosome bridge as well as “diagonal bridge”.(4) A few cells were found with lagged chromosomes, micronuclei and unbalanced segregation of the chromosomes. In the later stages of meiosis, well-spread chromosomal configurations were rare because of the extremely sticky nature of the chromosome. The number and ratio of abnormalities were analysed and the relationship between abnormalities and pollen sterility were discussed. It is concluded that the sticky nature of the chromosome is the main reason for abnormal meiosis of Aloe arboresens Mill.PMC and pollen sterility. More than 90% of matured pollen grains were sterile.