Compressed hydrogen is delivered by trailers in steel cylinders at 19.6 MPa in Japan. Kawasaki Heavy Industries, Ltd. developed two compressed hydrogen trailers with composite cylinders in collaboration with JX Nippon Oil in a project of the New Energy and Industrial Technology Development Organization (NEDO). The first trailer, which was the first hydrogen trailer with composite cylinder in Japan, has 35 MPa cylinders and the second trailer has 45 MPa cylinders. These trailers have been operated transporting hydrogen and feedstock to hydrogen refueling stations without the accident. This paper describes the safety design, including compliance with regulations, the influence of vibrations, and safety verification in case of a collision.