Abstract In this paper an extensive experimental campaign about the co-gasification of virgin wood biomass with organic and waste matrices in a full-scale downdraft air gasifier is presented. In particular, wastes from cherry processing, plastic wastes, sewage sludges and hazelnut shells were co-gasified with biomass adopting different mixtures. The syngas composition was continuously measured in order to assess the gasifier behaviour and performances using these mixtures. Results obtained mixing biomass with other feedstocks up to 60% (by mass) showed that the downdraft gasifier adopted, characterized by a patented internal air distribution system, was able to maintain a good gasification performance in terms of syngas lower heating value (LHV) (>5.18 MJ/Nm3), syngas flow rate (>400 Nm3/h) and cold gas efficiency (>71.9 %). A pseudo-kinetic model of the gasifier using Aspen Plus® code was developed as well. The model, calibrated with the experimental data, proved to fit the syngas composition and physical properties with satisfying accuracy. The numerical model confirmed its usefulness in predicting the performance of the gasifier as the operating parameters vary and clearly highlighted that secondary air flow and preheating of the gasifying air are effective ways for the enhancement of the cold gasification efficiency, which can reach values around 80%.