A closed-form solution using the distribution of fibre aspect ratios is proposed for predicting the thermal conductivity of aligned short fibre composites. The present model is the extended version of Hatta and Taya's model, where Eshelby's equivalent inclusion method modified for finite volume fraction of fibres is employed. The validity of using the average fibre aspect ratio for predicting the thermal conductivity is examined in terms of the distribution of the aspect ratios such as its average and standard deviation, fibre volume fraction, and constituents' thermal conductivity ratio. The guideline for the selection of either the actual distribution or the average fibre aspect ratio is presented in terms of the thermal conductivity ratio and the coefficient of the variation of the aspect ratio for the better prediction of the thermal conductivity of the composites.