High carbon to nitrogen ratio and complex lignocellulosic structure of wheat straw (WS) are the main hindrances in anaerobic digestion of this substrate. This research, conducted in two experiments, focused on the combined effect of co-digestion and thermal pretreatment of WS and sunflower meal (SM) on biogas production. In the first experiment, five co-digestion mixtures of WS and SM were made and assessed for biogas production. In the second experiment, the optimum co-digestion mixture selected from the first experiment was thermally pretreated at 120, 140, 160 and 180 degrees C and was evaluated for biogas production. Compared to control, the mixture M5 produced 61% higher biogas. It also showed better buffering capacity as compared to other mixtures and control. Combined effect of co-digestion and thermal pretreatment of the same mixture at 180 degrees C increased biogas yield by 94.3% as compared to control. Moreover, the experimental data obtained from both the experiments were validated using three different non-linear kinetic models. (c) 2020 Elsevier Ltd. All rights reserved.