In the year 2002, approximately 8 million maritime containers and 56,596 vessels entered the U.S. at more than 3,700 terminals and 301 ports of entry. Only 2% of these containers were inspected through x-ray equipment. More expensive radiation-detection equipments will be deployed to major U.S. seaports for use. Both x-ray and radiation-detection equipments conduct its inspection from the outside of a container, and cannot identify individual items inside. It also lacks the capability of item tracking and traceability along the shipping chain. A need exists for a system that can inspect containers without opening them on a mass scale at seaports. This paper describes a RFID and sensor based Container Content Visibility and Seaport Security Monitoring System under development that can fulfill this need. The System integrates the latest technologies in the fields of RFID, sensor, door tamper-proof device, and Wi-Fi communications to allow container contents to be identified and inspected automatically without opening it.