The function of tracheostomy is decreasing the amount of dead space, reducing resistance to airflow, providing protection against aspiration, enabling the patients to swallow without reflex apnea, providing access to the trachea for cleaning, providing a pathway to deliver medication, decreasing the power of the cough. The authors have compared the preoperative and postoperative data about the arterial blood gas analysis(ABGA) of tracheostomized patients as retrospective method in order to identify the efficacy of tracheostomy especially as a goal of the treatment in patients of respiratory failure. And the authors obtained the following results : 1) Tracheostomy was performed most frequently in the 6th decade group showing 21 cases(29.3%) and the 7th decade group showing 16 cases(22.2%) next in order. 2) Sex ratio between male and female was about 2 : 1. 3) The most frequent cause of the operation was cerebrovascular accident in 17 cases(23.6%), next was acute respiratory distress syndrome in 8 cases(11.1%). 4) According to the data of ABGA. (1) There was no statistical correlation between preoperative data and age(P>0.05). (2) With O₂ therapy, there was no difference between preoperative data and postoperative data. Without O₂ therapy, there was no difference, too. (3) There was no difference among the preoperative data, postoperative 1st day data and postoperative 3rd day data. After 7 days, there was difference in SO₂, PCO₂ and pH but no statistical significance.