In this paper, performance analysis of mobile phone with internal antenna for PCS band was carried out. The radiation patterns for antenna and mobile phone with internal antenna were simulated by using 3D simulation program, HFSS and SEMCAD. Radiation pattern variation was observed according to installation of LED circuit and ground pattern and by using simulation radiation pattern was improved. And radiation patterns of mobile phones with internal and external antennas were measured by using for field measurement system and chamber. Measured radiation pattern for mobile phone with internal antenna shows good agreement with simulation result. And the radio sensitivities of mobile phones with internal and external antennas were measured by using Agilent E5515C and chamber and compared. The measured radio sensitivity of mobile phone with internal antenna shows proper performances comparable to other model with external antenna. Measured result shows that the difference on averaged co-polar radio sensitivity is 0.12 ㏈.