Recently, there have been many theoretical and experimental studies on advanced composite materials (ACM) bridges in various fields over the world. Compared with a reinforced concrete or steel bridge, an ACM bridge has more advantages in strength, stiffness, transportation, and installation. Many demonstration projects have been carried out in the U.S, and Europe. They are also being developed and tested in South Korea. In South Korea the first of all ACM short-span bridge superstructures was installed on a public highway system in May 2002. Since these composite materials are new to bridge applications, reliable data is not available for their in-service performance. This paper describes in-service performance assessment of all ACM bridge superstructures. To investiga te its in-service performance, field load testing and visual inspections were conducted under an actual service environment. The p aper includes the presentation and discussion for ACM Bridge capacity rating based on the stress modification coefficients obtained from the test results. The test result indicates that the ACM bridge superstructure has no structural problems and is structurally performing well in-service as expected. The results may provide a baseline data for future field ACM bridge capacity rating assessments and also serve as part of a long-term performance of ACM bridge superstructure.