Uniform quasicubic alpha-Fe2O3 nanoparticles enclosed by six identical {110} planes were synthesized by a simple solvothermal method. TEM investigations revealed that they were formed through oriented attachment of primary nanocrystals assisted by Ostwald ripening, and PVP surfactant played an important role in control over the final morphology of the products. These quasicubic nanoparticles could catalyze oxidation of almost 100% CO at a temperature of 230 degrees C, much lower than those of nanophases with flowerlike, hollow, or other forms of irregular external morphologies having various crystal planes exposed to the gas, indicating that the external morphology and especially the exposure crystal planes of alpha-Fe2O3 nanocatalyst affect the catalytic activity more significantly than the traditionally accepted factors (such as high BET surface area, hollow structure, etc.) do for CO catalytic oxidation.