The study was aimed at the evaluation of the impact of drought stress on the efficiency of the photosynthetic apparatus of rye inbred line GULbw, evaluated based on measurements of chlorophyll fluorescence and gas exchange parameters, water balance, assimilation pigments and morphological characters, and by the analysis of the relationship between these parameters. The experiment was performed on the rye inbred line GULbw (original name: Gülzow 661-67, accession numbers: GueR 412; R 1599), obtained from the gene bank of The Federal ex situ Gene Bank for Agricultural and Horticultural Crop Species of The Leibniz Institute of Plant Genetics and Crop Plant Research Gatersleben. Because of drought, the PSII (photosystem PS II) performance index was reduced, and the decrease tendency of the PI (overall performance index of PSII) value intensified with the length of the stress period. The tested rye line did not exhibit any considerable variability of the maximum quantum efficiency of the PS II (Fv/Fm). Significant differences in the intensity of transpiration, stomatal conductance, and substomatal concentration of CO2 was determined on day 18 of drought. A significant positive value of the correlation coefficient r was found between PLSN, LSW, LSGN, LSGW, and E, gs, ci.