Sub-50nm spherical particles that exhibit single-molecule magnet (SMM) behaviour have been fabricated by direct precipitation of [Mn 12 O 12 (CH 3 COO) 16 (H 2 O) 4 ] clusters in a mixture of acetonitrile and toluene. The magnetic properties clearly indicate that particle formation does not affect the molecular composition of Mn 12 O 12 clusters, although some interesting differences appear when the magnetic behaviour exhibited by such nanoparticles is compared with a polycrystalline sample of [Mn 12 O 12 (CH 3 COO) 16 (H 2 O) 4 ].