Metered-dose inhalers have been used since the mid-1950s. They are compact, convenient and relatively inexpensive if used optimally. Poor inhalation technique is one of major problems among asthma (COPD) patients who use MDI. These problems has been present for long time and affect the outcome of chronic airway diseases. though, there was attention given to this problem through teaching inhalation technique but that wasn't enough to solve the problems. Therefore, adding spacer can dramatically decrease the amount of medicine deposited in the back of the mouth or on the tongue, allowing much more of the medicine to reach the lungs and decrease the doses needed to achieve a desired clinical response. However, current spacer design may need to be modified for better outcome.