Chlorophyll a fluorescence parameters (Fv/Fm, Fv/F₀ and Fvj) were used in testing wild oat (Avena fatua L.) resistance/susceptibility to fluazifop and quizalofop. Measurements of the selected fluorescence parameters were carried out at two terms: 24 and 48 hours after spraying resistant and susceptible biotypes of weeds with field doses of herbicides: Fusilade Forte 150EC and Targa Super 05EC. The obtained results indicate, that chlorophyll a fluorescence differed between resistant and susceptible biotypes. From all tested parameters Fvj is adequate for indicating wild oat resistance level to fluazifop and quizalofop.