Abstract Connecting cross laminated timber (CLT) panels to steel girders using mechanical connectors (e.g. screws and bolts) is an attractive and novel method for developing a fully prefabricated and sustainable hybrid steel-timber composite (STC) floor that can also facilitate future dismantling and recycling of its structural components. Since the structural performance of composite floors (including STC systems) is significantly influenced by strength and stiffness of slab-to-girder composite joints, this study characterises the load-slip behaviour and failure modes of steel-CLT timber composite joints by conducting push-out tests on three different types of STC connections with high-strength bolts, coach screws or a combination of glue and coach screws. Furthermore, the effect of reinforcing the CLT slabs by using steel nail plates on the strength and stiffness of STC joints is evaluated. Empirical models for capturing load-slip behaviour of steel-CLT composite joints with dowel (i.e. screw and bolt) connectors are derived from non-linear regression of experimental data and simple formulae for the strength and stiffness of steel-CLT composite joints with dowel connectors are proposed. Moreover, 1D beam on inelastic foundation finite element (FE) models of the dowel STC connectors are developed and validated against experimental results.