A physiological experiment was conducted with three yearling sheep, Stara Zagora x Pleven Blackhead crosses, to establish the effect of feeding Paulownia elongata leaves on some blood parameters. The trial consisted of two periods: control and experimental. During the control period, yearling sheep were fed a ration of 1 kg barley and 1 kg meadow hay, and during the experimental period-dried Paulownia elongata leaves. Blood samples were collected from v. jugularis externa before feeding and 2.5 hours after feeding during both periods after allowing 10-day adaptation to the respective diet. The studied parameters were erythrocyte counts, leukocyte counts, blood glucose, total protein, albumin and globulins. The intake of Paulownia leaves resulted in statistically significant reduction in erythrocyte (p< 0.05) and leukocyte counts (p< 0.001). This was most pronounced in the postprandial hours. Paulownia leaves also provoked increased total serum protein concentrations on the account of both higher albumin and globulins. The albumin/globulin ratio was 0.29 regardless of the type ofdietorthe time of sampling-prior to or after feeding.