For eradicating weeds in the crop field, a new herbicide propyl 4-(2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamino)benzoate (ZJ0273) is becoming popular in the rapeseed field in China.In order to developing a resistance/phytotoxicity monitoring tests for in field monitoring of growth status and phytotoxicity of this herbicide on oilseed rape crop, two leading commercial cultivars of oilseed rape viz.Brassica rapa cv.Xiaoyoucai and B.napus cv.ZS 758 were tested.Various concentrations of ZJ0273 (0mg/L, 100mg/L, 500 and 1000 mg/L were foliar applied at 3rd leaf stage of rapeseed plants.Imaging pulse-amplitude-modulated chlorophyll fluorometer (Imaging PAM) is being used to monitor the herbicide ZJ0273 resistance and phytotoxicity on oilseed rape.Measurements were carried out at 1, 3, 5 and 7 days after herbicidal treatment.The results revealed that maximum quantum yield (Fv/Fm), non-photochemical quenching (NPQ), electron transport rate (ETR) and photochemical utilization [Y(Ⅱ)] inhibition were significantly increased with herbicide application increasing, while photochemical quenching (qP), NPQ, Y(Ⅱ) and regulated heat dissipation [Y(NPQ)] were significantly decreased with herbicide application and increase in leaf age.However, the resistant B.napus species started to recover after 5 days.The growth response depicts the stunted plant growth especially at 1000 mg/L for both Brassica species.After being treated with 500mg/L and 1000 mg/L ZJ0273 (especially the latter), B.rapa seedlings were stunted severely at 5 days after the treatment, where the plants were not growing any more.The same typical symptom was also found in B.napus under 1000 mg/L ZJ0273 stress but not at 500 mg/L.Moreover, the concentration-inhibiting curves of Y(Ⅱ) and ETR suggested that 500 mg/L was a safer dose for B.napus.Chlorophyll fluorescence images of two rape species after 5 days treatment showed that the herbicide phytotoxicity was most severe in the 3rd leaf at high concentrations (500mg/L, 1000 mg/L in B.rapa).In contrast, different leaf age samples of B.napus did not reveal any visible variation for the Fv/Fm under various concentrations of ZJ0273.