The present study investigated the structural behaviour of steel-timber composite (STC) beams using numerical analysis. In the analysed system, a timber slab was connected to a steel beam with screws. Non-linear 3D finite element (FE) models of the STC beams were prepared. Both the dimensions of the STC beams and the parameters of materials were taken from literature. The steel beam was connected with the timber slab using zero-length wires, the behaviour of which allowed the slip between the steel beam and the timber slab. The slip modulus k0.4 was used to characterise the stiffness of the connector. The results of the numerical analyses were compared with the results from the laboratory tests presented in literature.