In order to extend the utilization of bamboo as a green building material, a new type of lightweight I-section bamboo-steel composite beam consisted of two pieces of cold-formed thin-walled steel channel and three pieces of bamboo plywood laths with adhesive bonding was developed and its mechanical properties was investigated. The results showed that the bamboo plywood and cold-formed thin-walled steel channel could form a good integrated composite cross-section. The failure modes, bearing capacities and deformation characteristics of the composite beams are associated with the flange thickness of the bamboo plywood, thickness of the cold-formed steel channel and the whole sectional dimension. Furthermore a simplified mechanical model and a calculation method were proposed based on the superposition principle and the predicted deformation and bearing capacity matched well with the experimental results, which indicate that the bamboo plywood can be used as a modern structural material. (C) 2014 Elsevier Ltd. All rights reserved.