The purpose of this study, was to investigate the effects of Onion Juice Administration (OJA) on Electrocardiogram (ECG) in dogs. Five clinically healthy street dogs were used in this study. Onion juice was given through oro-gastric tube of 400 g onion kg(-1) body weight dose in 500 mL water. Blood samples were collected at just before and after (6, 12 and 24th h) Onion Juice Application (OJA). PCV, heart beats counts and electrocardiograms of the animals in the same time were determined. PCV values gradually, decreased and these decreases were significant at 6th (p<0.01), 12th (p<0.01) and 24th (p<0.001) h after OJA. Bradicardia was observed at 6th (p<0.05) and 12th (p<0.001) h after OJA whereas tachycardia was observed at 24th h (p<0.001). Before and 6th h after OJA heart rates were within normal limits in this study. First degree heart block occurred 12th h after OJA and aritmia was obvious at this time. P-Q interval also increased. Bradicardia developed in some derivations. The mean heart rate was approximately 60 beats min(-1). Twenty-four hours after OJA tachycardia developed and the mean heart rate was 130 beats min(-1). In summary, OJA caused the anemia (reduction in the PCV values,) 1st degree heart block, tachycardia in dogs. Further studies on this issue, might be helpful for determining the effects of OJA on ECG in different species.