This is theoretical study of change in temperature of blood due to 4G mobile phone frequencies. We have done mathematical calculation of temperature change in blood of human body at different depths and different exposure time. Temperature change in blood tissues due to mobile phone radiation at different time exposure 10, 20, 30 40 50, and 60 minutes. The power of mobile phone handset is taken as 1.5 W. The distance inside the blood of 0.1mm to 0.5mm is taken for this study.