We have investigated nearly monodispersive MnO nanoparticles of 10 nm diameter by polarised neutron diffraction with XYZ-polarisation analysis. We found no long-range ordering down to 3.5 K. A broad magnetic peak appeared close to Q= (1/2,1/2,1/2) signifying short-range antiferromagnetic correlations. The correlation length was found to be about 2.4 nm at T=3.5 K. The correlation length decreases rapidly with increasing temperature and becomes about 0.7 nm at T=250 K. (C) 2010 Elsevier B.V. All rights reserved.