Biodiesel composition comprising of saturated and unsaturated fatty acid methyl esters has a significant influence on its properties and hence the engine performance and emission characteristics. This paper proposes a comprehensive approach for composition–property–NOx emission analysis for biodiesel fuels and highlights the pathways responsible for such a relationship. Finally, a procedure and a predictor equation are developed for the assessment of biodiesel NOx emission from its composition details. © 2016, The Institution of Engineers (India).