Blood gas analysis are highly susceptible to preanalytic error due to improper method of obtaining or handling the sample before analysis. To study the effect of air bubbles and time delay in estimation of blood gas, the samples were divided 3 groups, according to the method of stroage and the existence of air bubble, group 1, stored at 25±2C(room temperature) under anaerobic condition; group 2, stored at 0-4 degrees C(refrigerator) under anaerobic condition, group 3, stored at 0-4 degrees C under aerobic condition(10% air in blood). The samples were analyzed by time interval through 180 minutes in each group. The results were as follows: 1) Oxygen partial pressure decreased significantly after 20 minutes in group 2, whereas decreased significantly after 10 minutes in group 1 & group 3. 2) Carbon dioxide partial pressure increased significantly after 120 minutes in gorup 2 and 60 minutes in group 3, whereas decreased after 10 minutes in group l. 3) Blood pH decreased significantly after 60 minutes in all three Rroups. 4) Arterial oxygen saturation decreased significantly after 30 minutes in Rroup 1, 60 minutes in group 2 and 10 minutes in group 3. 5) Bicarbonate changes were not significant in all three groups clinically. From the above results, it is assumed that arterial blood samples should be analyzed whithin 10 minutes or cooled immediately.