This study deals with the crashworthiness of aluminum crash box for an auto-body with the various types of cross section. For the aluminum alloy, A17003-T7, the dynamic tensile test was carried out to apply for crash analysis at the range of strain rate from 0.003/sec to 200/sec. The crash analysis was carried out for four cross sections, square and hexagonal with and without ribs. The analysis result shows that the absorbed internal energy and the reaction force of crash box with rib are higher than that of crash box without rib. This result is due to the interaction between member and rib and the collapse of rib with the buckling mode. And the energy absorption is also affected by the cross section shape. Hexagonal cross section shows higher energy absorption and reaction force than square cross section.