This paper presents the manufacturing cost optimization of composite floor trusses. The composite floor trusses are designed to be built up of a reinforced concrete slab and steel trusses consisting of cold formed hollow sections. The optimization was performed by the nonlinear programming approach, NLP. An accurate objective function of the manufacturing material, power and labour costs was developed and applied for the optimization. Composite floor trusses were optimized according to Eurocode 4 for the conditions of both the ultimate and the serviceability limit states. A numerical example of the manufacturing cost optimization of a composite floor truss system, presented at the end of the paper, shows the applicability of the proposed approach.