Alpha linolenic acid (ALA) is an essential polyunsaturated fatty acids that can improve human health.Rapeseed is the second largest oil crop in the world but the ALA content in its seed fatty acids is only about 10％.Two rapeseed germplasms YH25005 and R8Q10 with high content (up to 21％) ALA were developed by intervarietal crossing.They were used as the maternal parent (P1) when crossed with a low ALA parent SW (P2) to produce the seeds of the F1 hybrid,F2,and backcrosses to P1 (BCP1) and P2 (BCP2).A multigeneration joint segregation analysis was conducted to determine major gene + polygene effects of the content of three major unsaturated fatty acids including oleic (OA),linoleic (LA) and ALA.The results showed that,although some genes favorable to ALA accumulation were not allelic in R8Q10 and YH25005,all the inheritances of OA,LA and ALA in YH25005 × SW and R8Q10 × SW followed a genetic model of \'two pairs of additive major genes + additive-dominant polygenes\'.It is suggested that the contents of OA,LA and ALA are closely related and the major genes in the parent SW containing loss-of-function mutations in FAD2 and FAD3 loci had strong effect to reduce ALA and elevate OA.However,total genetic effect of the polygenes was greater than that of the two major genes,especial on ALA content.It indicated that it is necessary to employ a larger F2 population to find the plant that accumulate enough minor-effect polygenes for high ALA content.The results are useful for high ALA rapeseed breeding and future work of gene mapping.