Cetane number is an important parameter in evaluating the quality of biodiesel fuel. Its determination is usually arduous and expensive, and the results obtained are not always accurate due to experimental error. This work is aimed at developing a relationship between the fatty acid methyl ester (FAME) composition and the cetane number (CN). Data were collected from the literature on the cetane number of various biodiesel fuels and their FAME composition. A regression analysis was performed on pure FAME to establish a relationship between the cetane number and FAME composition. An equation was developed relating the cetane number with the % composition by weight of FAME of biodiesel fuel. The predicted cetane number values compare well with the average measured cetane number values. This work establishes the general dependence of cetane number on FAME composition of biodiesels.