Abstract Twelve sources of equilibrium moisture content (EMC)/equilibrium relative humidity (ERH) data for rapeseed were identified from which 668 experimental points were extracted. Among them, ten sources covered a wide range of temperatures, thus producing 21 sub-sets of data suitable for the evaluation of EMC/ERH isotherm equations. Four commonly cited rapeseed EMC/ERH equations, i.e. modified Henderson, modified Chung–Pfost, modified Halsey and modified Oswin equations were compared for their ability to fit these data sub-sets based on the residual sum of squares (RSS), standard error of estimate (SEE) and mean relative deviation (MRD). The comparisons show that the modified Halsey equation is the best equation for describing the EMC/ERH isotherms of rapeseed. The modified Halsey equation was then used to fit the data sets merging all the data for adsorption, desorption and the combined data set in turn. The best fitted coefficients for both equilibrium relative humidity h r = f ( M,T ) and equilibrium moisture content M = f ( h r ,T ) are given, where T is the temperature. These fitted equations are based on a large data set and therefore provide a useful basis for future work on drying and storage of rapeseed.