Hybrid structural systems assembled connecting steel elements and cross-laminated timber panels (CLT) can be a valid alternative to traditional systems in the construction of residential buildings. Such systems can combine the industrialized construction technology typical of steel systems with the advantages offered by CLT panels, namely lightness and geometric stability. Moreover, CLT panels are timber-based products, and wood is recognized as an eco-friendly and eco-compatible material. In hybrid structural systems, the seismic-resistant capacity of the structure can be achieved by ensuring an adequate transmission of actions among the resistant elements, namely plain timber panels (floor and wall) and steel frame elements (beams and columns). Specifically, the interaction between the steel frame and the wood panels shall ensure both horizontal and vertical bracing to floors and walls, respectively. The work presented hereafter concerns the study of the connections to be used among the individual building components of the horizontal elements, with the aim of developing an effective collaboration among the materials, maximizing the level of prefabrication and industrialization of the final components. In particular, the preliminary results of the experimental tests carried out on full-scale steel-to-timber floor specimens, loaded by in-plane actions, will be presented.