Résumé : Accurate predictions of nitrogen oxides (NOx) are crucial for the design of low-emissions combustion technologies and require a truthful description of chemical kinetics and underlying thermo-chemical field. Nowadays, uncertainty remains in the reaction rates of different pathways of NOx formation. Experiments in simple systems, such as 1D flat premixed laminar flames, are necessary to shed light on the NOx formation process. However, experimental uncertainty cannot be avoided and influences the subsequent NOx formation modelling. In this context, forward propagation of experimental and kinetic uncertainties can be beneficial to assess their impact on the predictions of NOx emissions. In this work, forward Uncertainty Quantification (UQ) is performed via Polynomial Chaos Expansion (PCE), based on a sparse grid, to quantify the influence of the variability of temperature measurements and kinetic parameters on NO predictions in H2/CH4/CO-air 1D premixed laminar flames at low pressure, without and with 1.12% of benzene (C6H6) in the fuel blend. A significant uncertainty affects the prediction of NO for all the investigated flames. The measured temperature, with its uncertainty, is proven to be one of the most sensitive factor affecting the prediction of NO, particularly for the flames operated in lean and stoichiometric conditions. The results demonstrate that an accurate quantification of the uncertainty affecting the temperature measurements is critical for the development of predictive NOx formation models.