This paper presents an analysis of the effect of fuel additives on nitrogen oxide emissions from biomass combustion in a laboratory tube furnace. The analysis was performed for two mass fractions, i.e. two aluminosilicate minerals from kaolinite group – kaolin and halloysite. Both aluminosilicates are the subject of research carried out by scientists from the Silesian University of Technology as substances that have a positive effect on the combustion process, i.e. reduce the fouling effect in the boiler heating surfaces and improve the quality of combustion by-products of, which include fly ash. It is very important because while the Circular Economy is becoming a priority area, ash is a potential source of raw material that until recently was considered as waste and the spectrum of its reuse was quite narrow. This analysis is intended as a laboratory test of the effect of the use of additives on NOx emissions from biomass combustion and stems from the inconclusive observations made when studying the effect of additives on other properties of the combustion process. It was observed then that the only negative effect of using aluminosilicates was a slight increase in NOx emissions. The present work clarifies these observations.