A dwarf mutant ÔNDF-1Õ, approximately 70 cm high, was derived from a 200-cm high doubled haploid (DH) line Ô3529Õ (Brassica napus), seeds of which were jointly treated with chemical inducers and bombardment of fast neutron. The leaves of the ÔNDF-1Õ mutant were wrinkled and thicker compared with the wild-type control. The mutant had much lower values than its original parents for all agronomic traits, except for its seed weight. A genetic analysis revealed that dwarfism is under the control of a major gene (designated as ndf1) with a mainly additive effect and non-significant dominance effect. Because of the high level of resistance to lodging, breeding programmes for double low dwarf oilseed rape and heterosis utilization were initiated. Some new dwarf strains with improved agronomic performance were developed. The hybrid of the cross between the tall parent and the dwarf line showed increased harvest index and significantly higher seed yield than the tall parent or the control variety ÔZhongyou 821Õ and presented an estimated heterosis vigour rate as high as 12.5-25.8%. The dwarf trait will be a promising marker for a simple, economic and efficient way to control the purity of F 1 hybrid varieties in hybrid production of B. napus.