Agglomeration is a common phenomenon in many processes. The mechanical properties of agglomerates strongly depend on their structures. This paper presents a numerical study of the agglomeration of fine particles down to 1 ฮผm in size based on the discrete element method. The agglomerates were formed with particles initially generated randomly in a spherical space and then packed under an assumed centripetal force. Agglomerate structure, packing density, coordination number and tensile strength were analysed with particular reference to the effect of particle size associated with the van der Waals attraction. The results showed that both the packing density and coordination number of the agglomerates decay exponentially to their limits as agglomerate size increases. The tensile strength of the agglomerates was calculated from the simulations and shown to decrease with the increase of particle size. The strength was also estimated from the Rumpf model supported by the empirical equations formulated based on the present simulation results. The good agreement between the results from the simulations and the estimation indicates that the equations are useful to facilitate engineering applications.