Chlorophyll a fluorescence can provide insight into the ability of plants to tolerate environmental conditions that can damage photosynthetic apparatus and decrease yield. The aim of the study was to determine the relationship between chlorophyll a fluorescence parameters and yield components of oat DH lines. All DH lines significantly differed in chlorophyll a fluorescence parameters and yield components. The overall performance index of PSII photochemistry (PI), showed the highest variation between DH lines, whereas the lowest had the ratio of variable to maximum fluorescence (Fv/Fm). The highest differences were observed in the number of grains per plant (21.3 to 600). Thousand-grain weight varied from 17.82 g to 41.01 g and the biomass from 8.01 g to 29.31 g. The highest negative correlations were found between Fv/Fm, Area (pool size of electron acceptors from PSII), PI and grain number per plant and biomass. Positive correlations were observed between light energy absorption (ABS/CS), grain number per plant and biomass, as well as the amount of excitation energy trapped in PSII reaction centers (TRo/CS) and biomass. Principal component analysis of chlorophyll a fluorescence parameters, together with yield components, discriminated two oat DH lines groups according to their photosynthetic efficiency and yield.