Dwarf germplasm are valuable in breeding programs.We found a dwarf mutant from the inbred line K36 during multiplication in 2002.A stable inbred Ai 2003 was obtained after successive selfing.It was 62.1cm in plant height with good agronomical performance in Beijing.The test for response to gibberellin(GA) in different stage and dosage showed that Ai 2003 was not sensitive to GA.In order to understand the genetic control of this dwarf material,several crosses between Ai 2003 and normal inbred lines were undertaken to produce F1,F2 or BC1 families.The results showed that this dwarf germplasm was controlled by a major single nuclear recessive gene,which was different from gene Dwarf8(dominant) reported previously.