To achieve a mass goal and minimize the bell mouthing phenomenon of Passenger Air Bag Housing which takes place when the air bag is in explosive action and detrimental to the safety of passenger side because excessive canister bell mouthing may distort and crash the top surface of instrument panel, a study on the replacing process of a PAB housing to a different material and process was performed. The explosive action of current steel PAB housing was firstly analized to evaluate the reaction forces transferred through the PAB and find out the adaptable material for replacing process. Due to the properties among the die casting alloys, the AM60B alloy was chosen for our new material for PAB housing. Then, stress analysis by the finite element method was performed for a design modification of magnesium one piece housing. For the fabrication of a magnesium housing, a 350 ton hot chamber die casting machine was used and its optimum operating conditions and tool design were obtained from the casting process simulation. With a magnesium PAB housing, various tests such as severe deployment test, head impact test, and sled test were carried out for the verification of its quality and it was found that all test results met the test standards of Hyundai Motor Co.. From this study, we achieved a reduced bell mouthing amount by 50% and 1Kg weight saving over conventional steel housing.