A method for forming an ultrafine particle brittle material at low temperature which includes the steps of applying a mechanical impact force or a pressure to a ultrafine particle brittle material so as to have a percentage in the ultrafine particles having a primary particle diameter less than 50 nm in all the particles of 10 to 90%, subjecting the resulting brittle material to a heat treatment at a temperature not higher than the sintering temperature thereof so as to have the above percentage of 50% or less, and then applying a mechanical impact force not less than the crushing strength to the resultant material, to crush the material, thereby joining the ultrafine particles in the brittle material with one another, to form a formed article of the ultrafine particle brittle material; and an ultrafine particle brittle material for use in the method.