BACKGROUND OF STUDY: For the past 10 years, accidents and trauma are ranking third in the cause of Mongolian population’s death. Russian scientists have defined that skull and brain trauma comprise of 40% of the total traumas and is one of the serious injuries that have damaging effect to the health. Defining its creation, injury period, death cause in the leading direction of science of forensic medicine in our country are still the urgent issues. Nowadays little research which studied case mortality due to accident and trauma has been studied, this became background of our research work. PURPOSE OF STUDY: To study cause and peculiarity of pathology of case mortality due to brain trauma, in the condition of our country and to consider the result. OBJECTIVE OF STUDY: To study the cause, some risks of head injury. To define pathology of case mortality due to head injury. MATERIAL AND METHODOLOGY: We did retrospective study in 555 case material of an autopsy of case mortality of head injury of forensic medicine and research department of national institute of forensic science. Statistical work out was done by Microsoft excel and extensive index. RESULT OF STUDY: 84.5% (n=459) is male and 15.5% (n=86) is female out of our 555 involved cases and the gender ratio is 5:1. The most or 81% of the research participants had head injuries due to hitting with firm and dull stuffs and 15.9% head injury as a result of traffic accident follows in the second place. To analyze from the characteristics of mortality, 93% is subarachnoid hemorrhage, subdural, epidural hematoma, 64% is brain tissue injury were detected. CONCLUSION: Young manhood men mortality that has head injury resulted from the firm and dull things occupies most of the percentage in our research. The head injury can lead to the mortality of his ordinary process.