This paper presents the early detection of breast cancer as it detects the presence of tumor in the breast tissue using a Rectangular Patch Microstrip Antenna(RMSA) operating at 2.45 GHz. To enhance the impedance matching insect feed is used. To maintain the specific absorption rate(SAR) within the permissible range, a slot is introduced in the ground plane. The antenna is designed using FR4epoxy material. For the early detection of breast tumor parameters such as Voltage Standing Wave Ratio(VSWR), return loss(RL), Bandwidth has been observed. SAR has been taken under consideration while stimulating the antenna on breast phantom with and without tumor using High Frequency Simulation Software (HFSS). Resonating frequency of the antenna is 2.45 GHz and the VSWR=2 bandwidth is 40 MHz that means the bandwidth is approximately 1.63%. According to Federal Communications Commission (FCC) in the US has set a SAR level of 1.6 W/Kg and the same measurement is allowed in India. The antenna designed in this paper has a SAR value of 1.2 W/Kg without tumor and 1.4 W/Kg with a tumor which is in the permissible range. Due to the permissible range of SAR value and sufficient bandwidth proposed RMSA is used to detect tumors in the breast at an early stage.