The presented article describes the design and strength analysis of the frame of the Mars rover, which will start in the European Rover Challenge. The shape of the frame is determined by the six-wheeled rocker-bogie suspension chosen for the project, which is characterized by high stability and even distribution of wheel pressure on the ground and a reduction in the vibration frequency of the frame in which the vehicle electronics are located. The adopted slants counteract the swinging frame on the suspension, which has been checked by kinematic analysis. The design uses the concept of a frame structure made of sandwich walls, consisting of: 3D printed elements - an openwork grille with a honeycomb structure, a low-pressure foam filler and a carbon composite made of a combination of three layers of carbon fiber mat with a 1z1 weave and 0/45 /90 orientation with Epidian 5 epoxy resin ensuring equal spacing between the layers. Such a combination of materials allowed for a very durable and light structure with a significant reduction in weight compared to the original concept - an aluminum frame. A "cross"-shaped support element was also used, connecting the upper part of the frame with the lower one - also made in the 3D printing technique, which is also a link between the frame and suspension. The analysis showed that the materials and sections of structural elements adopted for the project are appropriate for the assumed load. In the case of unloading from the manipulator, the authors proposed to increase the safety factor due to the possibility of an additional load from dynamic forces. In places where reduced stresses reach increased values, additional reinforcements are provided.