This study was carried out to determine the effects of green tea on Electrocardiography (EKG) of Guinea pigs exposed to a 900 MHz electromagnetic field emitted by mobile phones. Because green tea has a beneficial effect on endothelial function, tea consumption is associated with decreased cardiovascular risk. Twenty-eight healthy guinea pigs weighing 600-800 g were used. After one week adaptation period, animals were randomly divided into four groups. Four experimental groups labeled as controls (Group A), irradiated (Group B), irradiated receiving green tea extract (Group C) and green tea only (Group D) were formed with seven randomly chosen animals. Group A and D were housed in a separate room without exposing EMF of mobile phones. Irradiation was accomplished by exposing the animals in Group B and C to a 900 MHz electromagnetic field from a 217-Hz pulse rate, 2-W maximum peak power mobile phone placed in the cage were the animals were kept. ECG of guinea-pigs in four groups was recorded by a direct writing electrocardiograph at the end of the 30-day experimental period during exposure to mobile phone. Sinus bradycardia (lower heart beat) and prolongation of the P-R interval was observed in Group B and C after exposure to electromagnetic field (P<0.05). Whereas the heart rate in the green tea extract supplemented group was close to the control group's level, it was found to have been the lowest in the only irradiated (Group B). We found measurable effects in the heart rate and P-R interval parameters in the EM-exposed guinea pigs. It was found that EMF exposure for 30 days have some effects on ECG findings of guinea-pigs. The results suggest that exposure of guinea pigs to EM fields can cause disturbances in autonomic cardiac regulation.