To establish a set of Chinese cabbage-cabbage monosomic alien addition lines,the backcross BC1 between allotriploid hybrids(AAC) and Chinese cabbage(AA) were used to screen monosomic alien addition lines by cytological observation.The results showed that chromosome numbers of BC1 varied from 20-29,the majority of those aneuploids were the plants with chromosomes 2n=23-24,reaching 51.44% of observing plants.Two monosomic alien addition lines were identified primarily by karyotype analysis and were named CO-5-1(Chinese cabbage with 5# chromosome from cabbage) and CO-8-2(Chinese cabbage with 8# chromosome from cabbage).