Aims:  Wild rape (Brassica juncea var. gracilis), a wild relative of oilseed rape (B. napus), was chosen for a case study because gene flow from herbicide-resistant oilseed rape to wild rape rarely has been explored.  We asked a) are transgenic herbicide-resistant oilseed rape and wild rape sexually compatible, b) is the fitness of their F1 improved and c) is gene flow possible?Methods:  We used hand pollination to test sexual compatibility and examined resistance of the F1 by applying herbicide of 2 000 ìg a.i.&#8226;kg-1 with 0.1 L&#8226;m-2 volume at 3-4 leaf stage twice and by PCR and examining vegetative growth, pollen viability and seed setting rate.  Crossing from herbicide-resistant oilseed rape to wild rape also was tested under open pollination.Important findings:  Indexes of sexual compatibility of wild rape×glufosinate-tolerant oilseed and wild rape×glyphosate-tolerant oilseed were 13.87 and 13.83, respectively, under hand pollination, and these indexes were not significantly different from that of the female parent under self pollination and open pollination.  All F1 were significantly resistant to the corresponding herbicide.  Moreover, herbicide-resistant gene of F1 was confirmed by PCR and F1 of wild rape× glufosinate-resistant oilseed and wild rape×glyphosate-resistant oilseed produced 426 bp and 931 bp identical special band, respectively.  The fitness of the F1 changed compared with that of the female parent.  The germination rate of the F1 was similar with that of the female parent, >98%.  Due to taller individuals and larger leaves, the vegetative growth of the F1 was much better than that of the female parent.  However, pollen viabilities of both kinds of F1 were only half that of the female parent.  Furthermore, the seed number per silique of the F1 was very low, only 0.59 and 0.58 seeds per silique, respectively.  The cross rate of wild rape ×glufosinate-resistant and wild rape×glyphosate-resistant was 0.02% and 0.01 %, respectively, under open pollination.  Our study suggests the possibility of gene flow from transgenic rape to wild rape. The possibilities of gene flow from the two herbicide-resistant transgenic oilseed rapes to wild rape were similar under hand pollination or open pollination.  However, the effect of gene flow from transgenic herbicide-resistant oilseed to wild rape needs further research.