Recently, due to environmental concerns and dependence on depleted resources, the use of renewable resources has become important in the preparation of various industrial materials. The use of natural fibers instead of petroleum-based synthetic fibers traditionally used in the production of composite materials provides many advantages in terms of both environmental and cost. The utilization of agricultural wastes as natural fibers also contributes significantly to the reduction and reuse of wastes, which is one of the objectives of sustainable development. In this study, artichoke stem waste fibers reinforced polyurethane foam composites were obtained. The fibers were treated with alkaline surface treatment at different concentrations (5% and 10%) of sodium hydroxide (NaOH) and durations (5, 10 and 15 min). The optimal alkali method was determined and applied to the fibers and its effect on composites was also investigated. Treated and untreated fibers were combined with polyurethane (PU) matrix at different reinforcement ratios (5, 10, 15 and 20%) to produce bio-fiber based composites. Depending on these reinforcement rates and alkali treatment, the mechanical properties of composites such as strength, elongation and modulus were investigated. The composites, which have the best mechanical properties, were selected and these composites were evaluated in terms of thermal and sound insulation with considering their morphological properties. It has been determined that artichoke stem waste fibers can provide good mechanical, thermal and sound insulation properties in the composites, and thus it has been found that great advantages can be achieved in terms of cost and ecology.