Mobile phones have become indispensable as communication tools; however, to date there is only a limited knowledge about interaction between electromagnetic fields (EMF) emitted by mobile phones and auditory function. Aim of the study: The aim of the study was to assess changes in the auditory system of guinea pig animals due to direct exposure to activated mobile phone waves using brain stem evoked response audiometry (BERA) and scanning electron microscopy(SEM). Material and methods: This study is conducted on 60 guinea pig animals. Their outer and middle ears were confirmed to be healthy by otomicroscopy. Divided into 4 groups each group composed of 15 animals : Group A serving as control. Group B exposed to activated mobiles by continuous calling and redialing from land phone while the phone is in the silent mode , 3 hours/day for 15 days . Group C exposed for 30 days . Group D exposed for 45 days . We developed a glass cage to accommodate the animals and to fix the mobile phone Ericsson T18s with cover over the key pad over the animal´s head. All animals are subjected to brain stem evoked response audiometry (BERA) bilaterally at the start of the study then each group re-examined every 2 week according to the duration of the study group. After last (BERA) 3 animals of the control group and 5 animals of each study group are sacrificed and cochlea removed for examination using scanning electron microscopy (SEM). Results : results of (BERA): Group B threshold was near group A control group with no statistically significant differences p>0.05 . In group C threshold was higher than groups A&B but this increase was non significant p>0.05. Group D there was significant increase in threshold (p value