Steel-timber composite (STC) floors are gaining popularity for residential and commercial buildings worldwide. Adding steel joists to wood-based panels is an attractive option for some designers to increase the span of timber floors. However, there is often a serviceability (vibration) concern with timber composite floors. It is well-known from the literature that human comfort due to vibration is subjective, and people's perception of comfort varies. Nevertheless, structural engineers still need to consider vibration in designing composite timber floors according to various standards and guidelines, especially when comparing two alternative designs. The study investigates the vibration behavior of STC floors under footfall force using a numerical model validated by experimental data. Transient finite element (FE) analysis is conducted to simulate human walking on the floor. The study also discusses acceptability of STC floors according to guidelines and building codes (e.g. AISC Design Guide 11, ATC, CLT Handbook, Eurocode 5). Lastly, the effects of various design parameters, such as CLT thickness, damping ratio, and CLT-to-CLT connection, on the vibration behavior of the composite timber floor are assessed.