Previously reported computer modelling of agglomeration of micrometre-sized aluminium particles during the combustion of composite solid propellants fails when applied to nano-aluminium particles because of the enormous number of the latter particles. A modified algorithm for three-dimensional casting and burning of composite propellants containing nano-aluminium particles on the computer is developed in the present work. In this, a regular grid is constructed overlaying the computer cast of coarse and fine ammonium perchlorate (AP) particles in the propellant, and the nano-aluminium particles are placed at randomly selected grid points outside of previously placed AP particles. Moreover, this is done one grid layer at a time in the burning direction to save computer memory. Further, since the burning surface is regressed at known burning rates over a larger step size than the above grid spacing, all the nano-aluminium particles located at grid points within one step of surface regression are lumped together and represented by an equivalent micrometre-sized particle. The agglomeration algorithm previously reported is then applied to this representative computer propellant cast. Results are compared with previously reported experimental data for two propellants with different coarse AP particles, one of them at three pressures. The predicted agglomerate size distribution agrees well with the experimental data. © 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.