Infant carriers play an important role in protecting child occupants from severe injuries caused by collisions, but the tension of harness webbing cannot be controlled properly most of the time. Infant carrier's user manual or instruction generally contains little information about the extent to which the adjusting belt should be pulled to cause the necessary webbing tension, and it is often neglected that the infants should be restrained securely. In order to improve public awareness, it is important to ascertain the effect of infant carrier's webbing tension on the occupant's chest accelerations. A testing scheme including 12 dynamic tests was devised and conducted, and test conditions were controlled strictly to ensure the accuracy and objectivity of results. P1.5 dummy's resultant and vertical chest accelerations were collected and analyzed. Both ISOFIX installation and seat belt installation methods were taken into consideration without lack of generality. Based on experimental validations, the relation between webbing's tensions and chest accelerations in frontal crash accidents was verified. Furthermore, suggestions were made about adjusting the webbing tension and the proper use of infant carriers.