Highly crystalline gamma-Fe2O3 nanoparticles with narrow size distributions that are coated with 1-undecanesulfonic acid were synthesized via two distinct approaches using oxidation and site-exchange reactions. However, similar nanocrystals protected with 1-octanol could only be achieved via the site-exchange method, while the oxidation approach led to Fe2O3 nanoparticles of poor crystallinity and size uniformity. Our magnetization measurements confirmed the superparamagnetic nature of our Fe2O3 nanoparticle products and the effects of the coating materials on magnetization properties. (C) 2003 Elsevier Science (USA). All rights reserved.